- Key Information
- Tony's story
What should I do?
If you think you have this condition you should see a doctor within 48 hours.
How is it diagnosed?
Your doctor might suspect ulcerative colitis based on your symptoms and physical examination findings. A sigmoidoscopy test (where a small camera is inserted into your back passage) is used to look for signs of ulcerative colitis. A sample from your colon may be taken during the procedure for further analysis. Blood tests might also be recommended to check for any complications of ulcerative colitis.
What is the treatment?
Ulcerative colitis is a long-term condition and treatment depends on the severity of your symptoms.
If you have flare ups with bouts of diarrhoea, you might be prescribed:
- a course of corticosteroids
- long-term medication which lowers the activity of your immune system to prevent flare ups.
When to worry?
If you develop any of the following symptoms then please seek medical help immediately:
- severe diarrhoea
- unable to eat or drink
- severe abdominal pain
- abnormally fast heart rate.
Ulcerative colitis is a long-term (chronic) condition affecting the colon.
- bloody diarrhoea
- abdominal pain
- a frequent need to go to the toilet
- weight loss
These can range from mild to severe, with the condition being unpredictable. Symptoms can flare up and then disappear (known as remission) for months or even years.
Read more about the symptoms of ulcerative colitis.
There is currently no cure for ulcerative colitis so the aim of treatment is to relieve symptoms during a flare-up and prevent symptoms from returning during remission – this is known as maintenance therapy.
Medications such as aminosalicylates and corticosteroids (steroid medications) are used for this.
Mild to moderate "flare-ups" can usually be treated at home. A severe flare-up needs treating in hospital as there is a chance of serious complications developing.
Surgery may be required to remove a section of the colon, if medication fails to work.
Read more about treating ulcerative colitis.
What causes ulcerative colitis?
Ulcerative colitis is thought to be what is known as an autoimmune condition. This means the immune system – the body’s defence against infection – goes wrong in some way and attacks healthy tissue.
One theory is the immune system mistakes harmless bacteria inside the colon as a threat and attacks the tissues of the colon, causing it to become inflamed. In severe cases, painful sores may form which bleed and produce mucus and pus.
Exactly what causes the immune system to behave in this way is unclear. Most experts think a combination of genetic and environmental factors is involved.
Read more about the causes of ulcerative colitis.
- inflammation of the bile ducts (tubes that transport bile out of the liver) – this is known as primary sclerosis cholangitis and can cause symptoms such as itchy skin and tiredness
- gases becoming trapped inside the colon, causing it to swell – this is known as toxic megacolon and requires emergency treatment as it can be life-threatening
People with ulcerative colitis also have an increased risk of developing bowel cancer. Because of this, regular bowel cancer check-ups are recommended.
Read more about the complications of ulcerative colitis.
Who is affected
Ulcerative colitis is an uncommon condition.
The condition normally appears in a person between the ages of 15 and 30.
It's more common in white people of European descent – especially those descended from Ashkenazi Jewish communities – and black people. The condition is much rarer in people of Asian background. The reasons for this are unclear.
Both men and women seem to be equally affected by ulcerative colitis.
The outlook for most people with ulcerative colitis is usually quite good. Symptoms are often mild to moderate and can be controlled with medication.
However, an estimated one-in-five people with ulcerative colitis have severe symptoms that fail to respond to medication. In these cases, it may be necessary to surgically remove the colon.
Anus The anus is the opening at the end of the digestive system where solid waste leaves the body. Chronic Chronic usually means a condition that continues for a long time or keeps coming back. Disease A disease is an illness or condition that interferes with normal body functions. Genetic Genetic is a term that refers to genes- the characteristics inherited from a family member. Inflammation Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area. Pain Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged. Remission Remission is when the symptoms of a condition are reduced (partial remission) or go away completely (complete remission). Stools Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement. Ulcers An ulcer is a sore break in the skin, or on the inside lining of the body.
These can vary depending on how much of the colon is affected and the level of inflammation.
Common symptoms include
- abdominal pain
- bloody diarrhoea with mucus
There may also be
- tiredness and fatigue
- appetite and weight loss
- anaemia (shortness of breath, irregular heartbeat, tiredness and pale skin)
- a high temperature (fever) of or above 38C (100.4F)
- a constant desire to empty the bowels (known as tenesmus)
Symptoms are often worse first thing in the morning.
Many people living with the condition will have long periods of months or years where they experience very few, or no, symptoms. However, in all cases, without treatment symptoms will eventually return.
No specific trigger that causes the return of symptoms has been identified, although it is thought stress may play a factor.
When to seek medical advice
If you experience a severe flare-up of symptoms you may need to be admitted to hospital as a precaution.
A severe flare-up is usually described as passing six or more blood stools in one day and having symptoms that suggest you are very unwell such as fever, rapid heartbeat and anaemia.
If you think you may be having a severe flare-up, contact your doctor or the doctor in charge of your care for advice.
Acute Acute means occuring suddenly or over a short period of time. Dehydration Dehydration is an excessive loss of fluids and minerals from the body. Diarrhoea Diarrhoea is the passing of frequent watery stools when you go to the toilet. Fatigue Fatigue is extreme tiredness and lack of energy. Fever A high temperature, also known as a fever, is when someone's body temperature goes above the normal 37C (98.6F). Loss of appetite Loss of appetite is when you do not feel hungry or want to eat. Pain Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
The exact cause of the condition is unknown, but researchers believe there are a number of factors involved. These are listed below.
Some researchers believe a viral or bacterial infection triggers our body's natural defence system against infection, the immune system.
The immune system responds to the infection by causing the inflammation associated with ulcerative colitis, but for some reason the immune system doesn't "turn off" once the infection has passed, and continues to cause inflammation.
Other scientists think no infection is involved and the immune system just malfunctions by itself.
A leading theory is that the immune system mistakes "friendly bacteria" found in the colon (which aid digestion) as an infection. So it tries to halt the spread of what it thinks is an infection by causing inflammation (swelling) of the colon. Conditions where the immune system attacks healthy tissue are known as autoimmune conditions.
It seems that genes you inherit play a role in developing ulcerative colitis. Studies have shown around one-in-six people with ulcerative colitis have a close relative with the condition. Also, levels of ulcerative colitis are a lot higher in certain ethnic groups than in others.
Researchers have identified several genes that seem to make people more vulnerable to developing ulcerative colitis, although exactly how they do this is still uncertain.
Where and how we live also seems to play a role in the development of ulcerative colitis. The condition is more common in urban areas in northern parts of Western Europe and America.
Various environmental factors have been suggested, including:
- air pollution
- diet: the typical Western diet is high in carbohydrates and fats, which may explain why Asian people, who tend to eat a diet lower in carbohydrates and fats, are less affected by ulcerative colitis
- hygiene: children are being brought up in increasingly germ-free environments, but it is possible the immune system requires exposure to germs to develop properly (this is known as the hygiene hypothesis, and has also been suggested as a possible cause for the rise in allergic conditions such as asthma)
However, no factors have been positively identified.
To diagnose ulcerative colitis, your doctor will first ask about your symptoms, general health and medical history. Then they will physically examine you, checking for signs such as paleness (caused by anaemia) and tenderness in the stomach (caused by inflammation).
The next step is to test your blood and a sample of your stool. Blood tests can show whether you have anaemia. There are also two specialised blood tests known as the erythrocyte sedimentation rate (ESR) test and the C reactive protein (CRP) test that look for changes in the blood that indicate disease and inflammation. Your stools will be checked for infection. X-rays may also be taken to help assess the extent of the condition.
The diagnosis will then need to be confirmed by examining the level and extent of the inflammation of the bowel. This is initially done by using a sigmoidoscope, which is a flexible tube containing a camera that is inserted into your rectum.
The procedure is not painful, though you may be given a sedative to relax you. It usually takes around 15 minutes, after which you can go home.
The sigmoidoscope is only capable of looking at the rectum and lower part of the colon. If it is thought your ulcerative colitis has affected more of your colon, another examination will be required. This is known as a colonoscopy.
A colonoscopy uses a longer and more flexible tube called the colonscope, which allows your entire colon to be examined.
Before having the examination it will be necessary for your colon to be entirely empty. Therefore you will be required to take strong laxatives beforehand.
Again, the procedure is not painful though you may feel initial discomfort. You will be given sedatives to help you relax. The procedure takes around half an hour, after which you will be able to go home.
Anus The anus is the opening at the end of the digestive system where solid waste leaves the body. Biopsy A biopsy is a test that involves taking a small sample of tissue from the body so it can be examined. Blood tests During a blood test, a sample of blood is taken from a vein using a needle, so it can be examined in a laboratory. Enema An enema is an injection of fluid into the large intestine/colon to empty the bowel. It can also be used to make the bowels show up more clearly in an X-ray. Inflammation Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area. Stool Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement. Ulcers An ulcer is a sore break in the skin, or on the inside lining of the body. X-ray An X-ray is a painless way of producing pictures of the inside of the body using radiation.
Once the diagnosis is confirmed, you may be referred to a gastroenterologist (doctor who specialises in conditions of the digestive system) so the severity of your condition can be assessed and a treatment plan drawn up.
The severity of the condition is judged by the following:
- how many times you are passing stools
- whether those stools are bloody
- whether you also have more wide-ranging symptoms such as fever, rapid heartbeat and anaemia (shortness of breath, irregular heartbeat, tiredness and pale skin)
- how much control you have over your bladder
- your general wellbeing
If your symptoms are mild you may not require specific treatment as mild ulcerative colitis often clears up within a few days.
Moderate ulcerative colitis is often treated using a medication called aminosalicylates. If this is not effective, alternatives such as corticosteroids (steroid medication) and immunosuppressants (medications that suppress the workings of your immune system) can be used.
Once your symptoms are under control it may be recommended you continue to take aminosalicylates as these can help prevent further flare-ups; this is known as maintenance therapy.
If you experience a severe flare-up you may need to be admitted to hospital where you can be given injections of corticosteroids or immunosuppressants.
There is also a relatively new type of medication called infliximab that can be used to treat severe ulcerative colitis where corticosteroids cannot be used for medical reasons.
Surgery may be recommended to remove a section of colon if medications fail to control symptoms or you are having frequent "flare-ups" of symptoms.
Treatment options are discussed in more detail below.
Aminosalicylates are the first treatment option for mild to moderate ulcerative colitis. They help reduce inflammation and can be taken:
- orally: as a tablet or capsule that you swallow
- as a suppository: a capsule that you insert into your rectum, where it then dissolves
- through an enema: where fluid is pumped into your colon
How you take aminosalicylates will depend on the severity and extent of your condition.
The side effects of aminosalicylates can include:
Corticosteroids (steroid medication) may be used if your ulcerative colitis is more severe or not responding to aminosalicylates. Steroids act much like aminosalicylates in reducing inflammation, except they are a lot stronger.
As with aminosalicylates, steroids can be administered orally, topically or through a suppository or enema.
Long-term use of steroids, especially oral steroids, is not recommended as they can cause potentially serious side effects. Therefore, once your colitis responds to treatment, it is likely you will need to stop using them.
The side effects of short-term steroid use can include:
Side effects of prolonged steroid use (more than 12 weeks) include:
- osteoporosis – weakening of the bones
- high blood pressure (hypertension)
- diabetes – or worsening of existing diabetes
- weight gain
- cataracts – where cloudy patches in the lens of the eye can make vision blurred or misty
To minimise the risk of prolonged steroid use, it is important that you:
- Eat a healthy and balanced diet with plenty of calcium.
- Maintain a healthy body weight.
- Stop smoking.
- Don't drink more than the safe limits of alcohol (recommended daily levels are three-to-four units of alcohol for men and two-to-three units for women).
- Take regular exercise.
You will also require regular appointments to check for high blood pressure, diabetes and osteoporosis if your treatment requires long-term use of corticosteroids.
You may be given immunosuppressants if your condition is still not responding to treatment, sometimes in combination with other medicines.
They may also be recommended if it is decided to withdraw your steroid treatment to reduce possible side effects. This is known as steroid-sparing therapy.
Immunosuppressants work by reducing or suppressing your body's immune system. This will then stop the inflammation caused by ulcerative colitis.
Immunosuppressants take a while to start working (typically two to three months).
The drawback is they affect your whole body, not just your colon. This may make you more prone to infection, so it is important to report any signs of infection, such as inflammation, fever or sickness, promptly to your doctor.
They can also lower the production of red blood cells, making you prone to anaemia. You will need regular blood tests to monitor your levels of blood cells and check for any other problems.
The preferred immunosuppressant used in the treatment of ulcerative colitis is a medicine known as azathioprine. This is because it rarely causes side effects in most people.
Long-term use of azathioprine has been linked to a small increase in the risk of cancer, particularly skin cancer.
Azathioprine is not normally recommended for pregnant women. However, if it is the only treatment that successfully controls your condition, it is likely you will be advised to continue taking it. Any risk to you or your child is far outweighed by the risks presented by ulcerative colitis.
Managing severe active ulcerative colitis
Severe active ulcerative colitis should be managed in hospital to minimise the risk of dehydration, malnutrition and potentially fatal complications such as your colon rupturing.
You will be given intravenous (injected directly into your vein) fluid to treat dehydration. The condition itself can be treated using injections of steroids or immunosuppressants.
Infliximab is a new type of medication only used to treat severe active ulcerative colitis if you are unable to take steroid medication for medical reasons, such as being allergic to it.
It works by targeting a protein called TNF-alpha, which the immune system uses to stimulate inflammation.
Infliximab is given through a drip in your arm over the course of two hours. This is known as an infusion.
You will be given further infusions after two weeks and again after six weeks. Infusions are then given every eight weeks, if treatment is still required.
Around one-in-four people have an allergic reaction to infliximab and experience symptoms such as:
- joint and muscle pain
- itchy skin
- high temperature
- swelling of the hands or lips
- problems swallowing
Symptoms range from mild to severe and usually develop in the first two hours after the infusion has finished.
Rarely, people have experienced a delayed allergic reaction days or even weeks after an infusion. If you begin to experience the symptoms listed above after having infliximab, seek immediate medical assistance.
You will be carefully monitored after your first infusion and, if necessary, powerful anti-allergy medication, such as epinephrine, may be used.
There have been a number of cases where infliximab has "reactivated" a previously dormant tuberculosis (TB) infection. Therefore, it may not be suitable if you have a previous history of TB. The same is also true with the viral infection hepatitis B.
Infliximab is also not recommended for people with a history of heart disease.
Infliximab will make you more vulnerable to infection, so avoid contact with people who have a known chickenpox or shingles infection.
It's important to report any symptoms of a possible infection, such as coughs, high temperature or sore throat, to your doctor.
Once the symptoms are in remission, taking a regular dose of aminosalicylates should help prevent symptoms reoccurring. If the condition frequently reoccurs, a regular dose of an immunosuppressant such as azathioprine may be recommended.
If your ulcerative colitis was extensive, a lifelong maintenance therapy is normally recommended.
If your ulcerative colitis was limited to a small part of your colon, you may be able to stop therapy, if two years pass without a return of symptoms.
If ulcerative colitis does not respond to intensive medical treatment, then surgery may be required.
You may also wish to consider surgery if your maintenance therapy is not working and the condition is affecting your quality of life.
Surgery involves permanently removing the colon – a colectomy. As part of the operation, your small intenstine will be re-routed from the colon so it can pass waste products out of your body.
This used to be achieved by carrying out an ileostomy, where an incision is made in your stomach and the small intestine is pulled slightly out of the hole and connected to a pouch (which collects waste materials).
However, in recent years, another technique known as the ileo-anal pouch has been increasingly used. This is an internal pouch constructed by the surgeon out of the small intestines and then connected to the muscles surrounding your anus. The pouch can be emptied in much the same way when you pass stools.
The advantage of this technique is that you are not required to carry an external pouch.
Read more about ileostomies and ileo-anal pouches.
Acute Acute means occurring suddenly or over a short period of time. Antidiarrhoeals Antidiarrhoeal medicine is used to treat diarrhoea. For example, dicyclomine. Corticosteroids Corticosteroid is a naturally occurring hormone produced by the adrenal gland, or a synthetic hormone having similar properties. It is used to reduce inflammation, so reducing swelling and pain. Enemas An enema is an injection of fluid into the large intestine / colon to empty the bowel. It can also be used to make the bowels show up more clearly in an X-ray. Inflammation Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area. Intravenous Intravenous (IV) means the injection of blood, drugs or fluids into the bloodstream through a vein. Remission Remission is when the symptoms of a condition are reduced (partial remission) or go away completely (complete remission).
Tony, who is in his forties, has had ulcerative colitis for more than 15 years. Having tried most medications, he is now on infliximab, which can only be given to certain patients. He is currently in remission, enjoys mountain biking and works full-time.
“I was about 28 when I started having bloody diarrhoea and passing mucus from my bowel. I’d lost weight and was bloated and getting stomach cramps. It was very worrying, so I visited my doctor.
“I was referred to hospital and had a colonoscopy, where the lining of your bowel is examined with an endoscope (flexible camera) and a small sample of the lining is taken. The test showed that I had ulcerative colitis.
“I was put on a medication called mesalazine, which helps reduces inflammation in your bowel. After a few years I went into remission (I no longer had any symptoms).
“But a while later the symptoms came back as the mesalazine became less effective in controlling them. The doctors tried me on a short course of steroid tablets and a steroid enema to suppress the inflammation.
“Ulcerative colitis is very unpredictable. Sometimes the symptoms can be mild and disappear quite quickly. It affects each person differently.
“My condition was at its worst about seven years later when I had another colonoscopy to see if there were any changes in the bowel lining. Then I went into remission again. I continued taking mesalazine, and I also tried azathioprine, which suppresses your immune system. For the next few years my symptoms came and went.
“In April 2006, the colitis flared up massively, after building up over several months. I lost a lot of weight, had to stay in bed for a few days, and I was constantly vomiting. I phoned NHS Direct, and was advised to go to hospital.
“I ended up staying in hospital for three-and-a-half weeks, recovering from the attack. I was given high-dose steroids through an intravenous drip, but after one week I had to stop because they weren’t working. The surgeon came and talked me through the next step – having a colectomy. I was devastated at the thought of having part of my bowel removed.
“Then they told me there was alternative treatment available. Infliximab is a fairly new and expensive drug that affects the immune response and reduces inflammation. It’s only used to treat people whose symptoms have not improved enough with other treatments, or who can’t be given other treatments for medical reasons. Fortunately, I was a suitable candidate.
“I am currently taking a course of infliximab and don't need surgery for now. It’s taken my disease into remission and everything’s OK at the moment, although I still get very tired.
“Although I’ve spent a lot of time off work, my lifestyle isn’t really affected. I work full-time and enjoy mountain biking and going to the gym regularly.”
Although diet does not seem to play a role in causing ulcerative colitis, it can help control the condition.
The following advice may help:
- Keep a food diary: you may find you can tolerate some foods, while others make your symptoms worse. By keeping a record of what and when you eat, you should be able to eliminate problem foods from your diet.
- Eat small meals: eating five or six smaller meals a day, rather then three main meals, may make you feel better.
- Drink plenty of fluids: it is easy to become dehydrated when you have ulcerative colitis, as you can lose a lot of fluid through diarrhoea. Water is the best source of fluids. Avoid caffeine and alcohol as these will make your diarrhoea worse, and fizzy drinks as these will cause gas.
- Food supplements: ask your doctor or gastroenterologist whether you need food supplements, as you might not be absorbing enough vitamins and minerals, such as calcium and iron.
Again, although stress does not cause ulcerative colitis, successfully managing stress levels may reduce the frequency of symptoms. The following advice may help:
- Exercise: exercise has been proven to reduce stress and lift your mood. Your doctor or gastroenterologist should be able to advise on a suitable exercise plan.
- Relaxation techniques: breathing exercises, meditation and yoga are good ways of teaching yourself to relax.
- Communication: living with ulcerative colitis can be frustrating and isolating. Talking to others with the condition can be of great benefit.
Primary sclerosing cholangitis
Primary sclerosis cholangitis (PSC) is a common complication of ulcerative colitis that affects about 1 in every 20 cases.
PSC is where the bile ducts become progressively inflamed and damaged over time. Bile ducts are small tubes used to transport bile (digestive juice) out of the liver and into the digestive system.
PSC does not usually cause symptoms until it is in an advanced stage. Symptoms can include:
- fatigue - extreme tiredness
- itchy skin
- weight loss
- high temperature (fever) of 38C (100.4F) or above
- jaundice: yellowing of the skin and the whites of the eyes
There is no direct treatment for PSC but medications, such as rifampicin, can be used to relieve many of the symptoms, such as itchy skin.
In more severe cases of PSC, a liver transplant may be required.
People who have ulcerative colitis have an increased risk of developing bowel cancer (cancer of the colon, rectum or bowel), especially if the condition is severe or extensive.
The longer you have ulcerative colitis, the greater the risk is:
- After 10 years the risk of developing bowel cancer is 1 in 50.
- After 20 years the risk of developing bowel cancer is 1 in 12.
- After 30 years the risk of developing bowel cancer is 1 in 6.
People with ulcerative colitis are often unaware they have bowel cancer as the initial symptoms of this type of cancer are similar to ulcerative colitis, such as blood in your stools, diarrhoea and abdominal pain.
Because of these issues you will probably be advised to have a colonoscopy every few years to check no cancer has developed. The frequency of the colonoscopy examinations will increase the longer you live with the condition.
To reduce the risk of developing bowel cancer, make sure you eat a healthy, balanced diet including plenty of fresh fruit and vegetables. It is also important to take regular exercise, maintain a healthy weight and avoid alcohol and smoking.
Taking aminosalicylates as prescribed should also help reduce your risk of bowel cancer.
Osteoporosis is a common complication affecting an estimated 1 in 6 people with ulcerative colitis.
Osteoporosis is a condition that affects the bones, causing them to become thin and weak. The condition is not directly caused by ulcerative colitis, but develops as a side effect of prolonged steroid use.
Although risks associated with steroid use are well-known, in some people long-term use of steroids is the only way to control symptoms of ulcerative colitis.
There are several medications, such as bisphosphonates, that can be used to strengthen the bones.
You may also be advised to take regular supplements of vitamin D and calcium, as both of these substances have bone-strengthening effects.
Read more about the treatment of osteoporosis.
Toxic megacolon is a rare and serious complication that occurs in approximately 1 in 20 of cases of severe ulcerative colitis. In severe cases of inflammation, gases can get trapped in the colon, causing it to swell. This is dangerous as it can:
- send the body into shock (a sudden drop in blood pressure)
- rupture (split) the colon
- cause infection in the blood (septicaemia)
The symptoms of a toxic megacolon include:
- abdominal pain
- high body temperature (40C or 104F)
- a rapid heart rate
Toxic megacolon can be treated with intravenous fluids, antibiotics and steroids. At the same time, a tube will need to be inserted into your rectum and colon so the gas can be drawn out and your colon decompressed.
In more severe cases, a colectomy will need to be performed.
Treating symptoms of ulcerative colitis before they become severe can help prevent a toxic megacolon from developing.
Emotional impact of ulcerative colitis
Living with a long-term condition that is as unpredictable and potentially debilitating as ulcerative colitis, particularly if it is severe, can have an emotional impact.
In some cases anxiety and stress caused by ulcerative colitis can trigger depression.
Signs of depression include feeling very down, hopeless and no longer taking pleasure in activities you used to enjoy.
If you think you might be depressed, contact your doctor for advice.
Read more about treating depression.
You may find it useful to talk to others affected by ulcerative colitis, either face to face or via the internet.
The site also contains a large range of useful information on ulcerative colitis and related issues.
Blood Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart. Deficiency If you have a deficiency it means you are lacking in a particular substance needed by the body. Immune The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses. Inflammation Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area. Joints Joints are the connection point between two bones that allow movement. Liver The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy. Pain Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged. Ulcerated An ulcer is a sore break in the skin, or on the inside lining of the body.