We all have times when we lack confidence and don't feel good about ourselves.
But when low self-esteem becomes a long-term problem, it can have a harmful effect on our mental health and our lives.
Self-esteem is the opinion we have of ourselves.
When we have healthy self-esteem, we tend to feel positive about ourselves and about life in general. It makes us able to deal with life's ups and downs better.
When our self-esteem is low, we tend to see ourselves and our life in a more negative and critical light. We also feel less able to take on the challenges life throws at us.
Low self-esteem often begins in childhood. Teachers, friends, siblings, parents, and even the media send us messages about ourselves, both positive and negative. For some reason, the message that you are not good enough is the one that stays with you.
Perhaps you found it difficult to live up to other people's expectations of you, or to your own expectations.
Stress and difficult life events, such as serious illness or a bereavement, can have a negative effect on self-esteem.
Personality can also play a part. Some people are just more prone to negative thinking, while others set impossibly high standards for themselves.
If you have low self-esteem or confidence, you may hide yourself away from social situations, stop trying new things and avoid things you find challenging.
"In the short term, avoiding challenging and difficult situations makes you feel a lot safer," says Chris Williams, Professor of Psychosocial Psychiatry at the University of Glasgow.
"In the longer term, this can backfire because it reinforces your underlying doubts and fears. It teaches you the unhelpful rule that the only way to cope is by avoiding things."
You may also develop unhelpful habits, such as smoking and drinking too much, as a way of coping.
To boost your self-esteem, you need to identify the negative beliefs you have about yourself, then challenge them.
You may tell yourself you are "too stupid" to apply for a new job, for example, or that "nobody cares" about you.
Start to note these negative thoughts and write them down on a piece of paper or in a diary. Ask yourself when you first started to think these thoughts.
Next, start to write down evidence that challenges these negative beliefs: "I am really good at cryptic crosswords" or "My sister calls for a chat every week".
Write down other positive things about yourself, such as "I am thoughtful" or "I am a great cook" or "I am someone that others trust".
Also write down good things that other people say about you.
Aim to have at least five things on your list and add to it regularly. Then put your list somewhere you can see it. That way, you can keep reminding yourself that you are OK.
"You might have low confidence now because of what happened when you were growing up," says Professor Williams. "But we can grow and develop new ways of seeing ourselves at any age."
Here are some other simple techniques that may help you feel better about yourself.
We are all good at something, whether it's cooking, singing, doing puzzles or being a friend. We also tend to enjoy doing the things we are good at, which can help to boost your mood.
If you find certain people tend to bring you down, try to spend less time with them, or tell them how you feel about their words or actions.
Seek out relationships with people who are positive and who appreciate you.
Professor Williams advises: "Be compassionate to yourself. That means being gentle to yourself at times when you feel like being self-critical.
"Think what you'd say to a friend in a similar situation. We often give far better advice to others than we do to ourselves."
Being assertive is about respecting other people's opinions and needs, and expecting the same from them.
One trick is to look at other people who act assertively and copy what they do. "It's not about pretending you're someone you're not," says Professor Williams. "It's picking up hints and tips from people you admire and letting the real you come out."
People with low self-esteem often feel they have to say yes to other people, even when they don't really want to. The risk is that you become overburdened, resentful, angry and depressed.
"For the most part, saying no doesn't upset relationships," says Professor Williams. "It can be helpful to keep saying no in different ways until they get the message."
We all feel nervous or afraid to do things at times. But people with healthy self-esteem don't let these feelings stop them from trying new things or taking on challenges.
Set yourself a goal, such as joining an exercise class or going to a social occasion. Achieving your goals will help to increase your self-esteem.
Help is available if you feel you need support to start seeing yourself in a more positive light.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.