Obsessive compulsive disorder (OCD) affects people differently, but usually causes a particular pattern of thought and behaviour.

This pattern has four main steps:

• obsession – where an unwanted, intrusive and often distressing thought, image or urge repeatedly enters your mind
• anxiety – the obsession provokes a feeling of intense anxiety or distress
• compulsion – repetitive behaviours or mental acts that you feel driven to perform as a result of the anxiety and distress caused by the obsession
• temporary relief – the compulsive behaviour brings temporary relief from anxiety, but the obsession and anxiety soon return, causing the cycle to begin again

Obsessive thoughts

Almost everyone has unpleasant or unwanted thoughts at some point in their life, such as a concern that they may have forgotten to lock the door of the house or that they may contract a disease from touching other people, or even sudden unwelcome violent or offensive mental images.

Most people are able to put these types of thoughts and concerns into context, and they can carry on with their day-to-day life. They do not repeatedly think about worries they know have little substance.

However, if you have a persistent, unwanted and unpleasant thought that dominates your thinking to the extent it interrupts other thoughts, you may have developed an obsession.

Some common obsessions that affect people with OCD include:

• fear of deliberately harming yourself or others – for example, fear you may attack someone else, even though this type of behaviour disgusts you
• fear of harming yourself or others by mistake or accident – for example, fear you may set the house on fire by accidentally leaving the cooker on
• fear of contamination by disease, infection or an unpleasant substance
• a need for symmetry or orderliness – for example, you may feel the need to ensure all the labels on the tins in your cupboard face the same way

Compulsive behaviour

Compulsions arise as a way of trying to reduce or prevent the harm of the obsessive thought. However, this behaviour is either excessive or not realistically connected at all.

For example, a person who fears becoming contaminated with dirt and germs may wash their hands repeatedly throughout the day, or someone with a fear of causing harm to their family may have the urge to repeat an action multiple times to try to "neutralise" the thought of harm. This latter type of compulsive behaviour is particularly common in children with OCD.

Most people with OCD realise that such compulsive behaviour is irrational and makes no logical sense, but they cannot stop acting on their compulsion.

Some common types of compulsive behaviour that affect people with OCD include:

• cleaning and hand washing
• checking – such as checking doors are locked, or that the gas or a tap is off
• counting
• ordering and arranging
• hoarding
• asking for reassurance
• repeating words silently
• extensively "overthinking" to ensure the feared consequence of the obsession does not occur – for example, if you fear you may act violently
• thinking "neutralising" thoughts to counter the obsessive thoughts
• avoiding places and situations that could trigger obsessive thoughts

Not all compulsive behaviours will be obvious to other people.

Related problems

Some people with OCD may also have or develop other serious mental health problems, including:

• depression – a condition that typically causes lasting feelings of sadness and hopelessness, or a loss of interest in the things you used to enjoy
• eating disorders – conditions characterised by an abnormal attitude towards food that cause you to change your eating habits and behaviour
• generalised anxiety disorder – a condition that causes you to feel anxious about a wide range of situations and issues, rather than one specific event
• a hoarding disorder – a condition that involves excessively acquiring items and not being able to throw them away, resulting in unmanageable amounts of clutter

People with OCD and severe depression also frequently have suicidal feelings.

Getting help

OCD can stop you carrying out normal day-to-day activities and can have a significant impact on your career, education and social life.

It is therefore important to seek help from your GP if you think you have the condition. With the correct diagnosis and treatment, you should be able to manage your symptoms and have a better quality of life.

You should also visit your GP if you think you may have one of the related mental health problems mentioned above, as these conditions may become more severe if they are left untreated and may make it more difficult for you to cope with your OCD.

Contact your GP or care team immediately if you are depressed and feeling suicidal. You can also telephone the Samaritans to talk in confidence to a counsellor on 08457 90 90 90. Alternatively, you can call NHS 111.

If you think a friend or family member may have OCD, it's a good idea to talk to them about your concerns and suggest they seek medical advice.

While it might seem natural to try to protect the person with OCD from their own fears, this is counterproductive because it means the problem is not resolved and there is no hope of moving on.

Read more about diagnosing OCD.