Pubic lice - also known as crabs - is an infestation due to a wingless insect. They cling tightly to the pubic hairs and may cause itching, especially when they bite.

How is pubic lice diagnosed?
By seeing the lice clinging to pubic hairs, which may be examined under a magnifying glass.

How is pubic lice treated?
You can buy products over the counter to treat them, or see your doctor for a prescription. The usual treatments are a lotion (for example, Quellada) or a special shampoo (for example, Prioderm). Follow instructions on the pack to make sure you treat yourself properly.

Your bedding and underclothes need to be washed at a temperature higher than 60C to kill off any eggs so you don't re-infect yourself. You will need to pluck up courage to tell your friends how to treat the lice, too. Try not to be embarrassed. It is relatively common and - although the bugs can be passed on sexually - you can also catch them through contact with clothes, sheets or towels used by someone who is infected.

If you're worried you have an STI or want to find out more, check out the symptoms, diagnosis and treatments for:

• Chlamydia
• Genital herpes (HSV)
• Genital warts
• Gonorrhoea
• HIV and AIDS
• Scabies
• Syphilis
• Trichomonas