"Personality traits fall on a continuum. In relation to personality disorder (PD), we mean people whose behaviour often, rather than occasionally, falls at the extreme," explains Dr Naomi Murphy, clinical psychologist, clinical director of the Fens Service for Men with Personality Disorder, and co-author of Treating Personality Disorder. "To be diagnosed with PD you must be over 18 and have experienced difficulties over several years and in multiple areas of your life."

PD affects three key areas, she reveals: "your inability to manage your emotions either by being easily overwhelmed or by switching off from your emotions; distorted beliefs such as a pronounced fear of rejection or belief that others can't be trusted; and difficulties in forming and maintaining relationships because of problems managing emotions and distorted beliefs."

There are some common signs someone with a personality disorder may show, says Isabel Clarke, consultant clinical psychologist for the italk service, and the Southern NHS Trust, and author of Comprehend, Cope and Connect. "Self-harm is common to relieve emotional pressure, while alcohol, drugs and casual sex are often used to numb difficult feelings. Others shut down altogether and avoid relationships."

There is no single 'cause' of a PD, and most experts agree it's a combination of three main factors.

• The environment you grew up in and what was happening during your childhood years. For example, a chaotic family life, bad experiences at school.

• Traumatic experiences in childhood and teenage years such as abuse, neglect, bereavement, involvement in an accident.

• Genetics.

The main types of personality disorder

A psychiatrist or clinical psychologist can diagnose PD. Experts use several guildelines to define the different forms of PD. One of the most commonly used is a set of guidelines which identify 10 types of PD, grouped into three clusters: 'suspicious', 'emotional/impulsive' and 'anxious/avoidant'.

"PD is most often diagnosed in your 20s and 30s, with the most common types being borderline personality disorder and antisocial personality disorder," says Murphy.

Suspicious

People with a 'suspicious' type of PD may seem eccentric and find it hard to relate to others. They see threats in everyday situations and find it difficult to trust. These include paranoid PD, schizoid PD and schizotypal PD.

Emotional/impulsive

Those with an 'emotional/impulsive' PD find it hard to control their emotions, act impulsively and find it hard to maintain relationships.

Someone affected by antisocial PD may often be in risky situations, be aggressive and frequently be in trouble with the law.

If you're affected by borderline personality disorder (BPD) (or emotionally unstable PD) you'll experience strong and rapidly changing emotions, a deep fear of being abandoned or alone, little sense of identity, difficulty in maintaining relationships and a feeling of emptiness much of the time. Selbstverletzung and suicide attempts are common.

Anxious/avoidant

People with 'anxious/avoidant' types of PD are introverted, anxious and fearful.

Someone with dependent PD has little self-confidence and allows others to take control. If avoidant PD is suspected, you'll have a constant fear of being 'found out' and rejected and will avoid relationships to prevent this. Someone with obsessive compulsive PD, by contrast, needs to be in control and is a perfectionist.

Specialists disagree over whether having an official diagnosis is helpful. "The problem with a diagnosis is that it is quite blaming," says Murphy. "It's still misunderstood and carries some stigma. However, a diagnosis is often the gateway to the right support and recovery."

"The main advantage of having a diagnosis is this is how our mental health services are set up - a diagnosis gives access to the right treatment," points out Clarke.

For Tilly, 21, a diagnosis of BPD at age 18 kick-started her recovery after years of mental health problems. "Little things used to make me explode with anger, I hated social interaction with people I didn't know, I was gripped with Angstzustände most of the time, heard voices and was feeling suicidal. To an outsider, it seemed like I overreacted, but really it was just that my emotions were much more intense. But then at other times, my feelings of emptiness had caused me to attempt suicide on many occasions or to harm myself just so I could feel something. I switched between feeling everything too intensely or feeling nothing at all."

Before being diagnosed with BPD, Tilly was diagnosed with Depressionen, mixed anxiety and depression and psychosis, while bipolar, Asperger's and ADHS were also considered.

"When I was first diagnosed at 18 in a psychiatric unit, I was in denial. Gradually, as I learned more about BPD and the criteria, I realised almost all my symptoms and behaviours matched those of people with BPD. Things began to fall into place, and it meant I could get the specialist help I needed," she reveals.

Tilly was referred to the Emerging Personality Disorder team at 18, and has since seen a support worker every week. She's also had dialectical behaviour therapy and cognitive analytical therapy.

"My emotions are still intense, but it takes less time to calm down than before. I am less impulsive and more able to use skills and techniques to help myself. I manage relationships better."

"PD is definitely something you can recover from and accept as being part of who you are. With help, you can learn to stop the unhealthy coping mechanisms and swap these for more helpful strategies," says Clarke.

Gesprächstherapien are the mainstay of treatment. "You should expect to receive an in-depth course of therapy as PD takes some time to treat properly. And you may well need to return to therapy several times and try different types," says Clarke.

Dialectical behaviour therapy (DBT) is commonly recommended, helping you learn to recognise and control your emotions and behaviour. While mentalisation-based therapy (MBT) is about being aware of what's happening in your own mind and that of others to help control distress. Cognitive analytical therapy (CAT) helps you to recognise relationship patterns that cause you problems. Schema therapy aims to strengthen ways of thinking that are helpful and change those which are not.

Medication is often used, although no drugs are specifically recommended to treat PD. It may help with symptoms of depression, anxiety, anger or psychosis. You may be offered antidepressants, mood stabilisers or antipsychotics.

People with severe and long-standing PD may be offered treatment in a therapeutic community. The idea is that you spend time with people experiencing similar difficulties and support each other, alongside group and individual therapy.