If it's not successfully managed, stress can lead to greater problems, writes Susan Edmunds.

Whether it's caused by the demands of a full-on job, the struggle to balance family and work commitments or a one-off event such as moving house, stress is familiar to most people.

Good or bad, when you face pressure, your body's instinct to defend itself kicks in. Stress is a natural response but if it goes on too long it can become a mental and physical problem. A lot of successful people say they are driven by stress - but how do you know when stress is changing from a positive, motivating force to a negative one?

Mary Grogan, of Change It Psychology, says psychologists refer to eustress (that results in increased productivity) versus distress (a long-term drain on your system).

"Eustress might be felt before an important performance - it can help us focus and perform well under pressure," she says. "Typically stress becomes a problem when it is affecting one or more areas of your life; for example you might be tired and irritable most of the time, which affects those you live with, so there are more fights, and this has become a regular pattern. The optimal amount of stress differs for each of us so we need to define it individually and not compare it with others."

The first step is to recognise you are stressed, and what you think might be causing it. Then work out what, if anything, is in your power to change. Can you break down a seemingly insurmountable problem into a series of more realistic ones, do more planning for an upcoming stressful event, resolve conflicts that are playing on your mind, increase the amount of exercise you do, or sleep and eat better?

Grogan says people should recognise the impact stress has on their lives and consider what it could be like in three or six months, if nothing changes.

"For most of us to change our behaviour, we need to recognise the current methods aren't working and it's worth spending time and energy figuring out methods that might be better," she says. "For example if you've noticed your hours of work have crept up in recent months, and your ability to exercise, eat healthily, and catch up with friends and family has decreased, ask yourself how long you think that is sustainable."

Once you know something has to happen, the next move is easier. If you know your job is causing your increased stress, for example, you can start making changes to fix it. Talk to your boss about limiting your overtime, or see if there are ways to make your workload more manageable.

But it can be easy to feel powerless if the thing causing most of your stress is out of your control. Grogan says this sort of stress can benefit from professional intervention: "Figure out which parts of a problem you might have to let go of. Remind yourself of the saying: 'Grant me the ability to change the things I can, serenity to accept the things I can't change, and the wisdom to know the difference'. You may need help coming to a point of acceptance with some thorny issues, such as people dying or being made redundant from your job."

Keeping an eye on the way you feel throughout the day can help you keep on top of stress. "Awareness of your moment-by-moment daily experience is something we teach to prevent stress. You can do this by being aware of small things throughout the day that change your mood from feeling okay to feeling down/anxious/stressed/angry. Notice the thoughts, body sensations and feelings that accompany these changes so you don't react, but respond effectively to whatever comes up."

Diaphragmatic breathing - deep breathing that expands your abdomen rather than your chest when you inhale - is a good way to calm down when you feel your stress levels increasing. Change the way you think, too. Grogan says. "Challenging catastrophic thoughts can be useful. If you think 'I will look like a fool doing this speech', try telling yourself, 'It's natural to be a bit nervous and that can help performance. Most people won't notice'."

Combat stress
* Work out the source of the stress.

* Identify the aspects that you have control over and take action, however small.

* Eat well, sleep well and get more exercise.

* Focus on details and slow down.

* Consider professional help to get over stressful things that are beyond your control.