Infestations with pubic lice (often called crabs) and scabies are very common amongst sexually active men and women, gay and straight, and are easily treated.

Pubic lice are small insects that resemble crabs because of their claws, which allow them to hold onto pubic hair (body hair near the genitals and anus). Although crabs are particularly fond of pubic hair, they can live in hair in other parts of the body, particularly the armpits, and even in the eyebrows and eyelashes, although this is uncommon.

Crabs are normally picked up and passed on during sex, though any form of intimate bodily contact can be enough to pass them on. They can also be picked up from sharing towels, bedding or clothing, but this is less common.

Some people notice the infestation within hours, but others do not become aware that they have crabs for several weeks. Crabs are very small and can be very difficult to see, but symptoms usually include an intense itching in the groin, and some people notice the lice eggs firmly attached to pubic hair. Small spots of blood may appear on underwear or sheets.

Lotions such as Derbac are available from chemists, without prescription, for getting rid of crabs, and these are also available free of charge from sexual health and GUM clinics. It is important to follow the instructions properly as improper use could mean that you fail to clear the infestation, and using too much could provoke an allergic reaction. Do not use Derbac or similar lotions after a hot bath.

Shaving pubic hair will not get rid of crabs. It is important to wash all clothes, towels and bedding you have used since you picked up crabs on a hot cycle when you start treatment. You should also ensure that your partner, or people with whom have had intimate bodily contact, or shared a bed, use treatment at the same time as you to avoid reinfestation.

Scabies is a skin disease caused by a mite that burrows under the skin causing intense itching, particularly at night. They are invisible to the naked eye, but leave red ‘track marks’ in the skin. Usually scabies affect the hands between the fingers, the genitals, breasts, buttocks, abdomen and feet.

It is easy to pick up scabies, any skin contact is enough, and sharing towels or bedding is enough for transmission to occur.

The same lotions used to treat crab infestations are also effective against scabies, although it may be necessary to leave the lotion on the body for longer (usually 24 hours). It should be applied to the whole body, other than the face and scalp, and reapplied to the hands after hand-washing if this is an area of infestation. After treatment, the itch can get worse temporarily. In this case, hydrocortisone cream can be applied, and the itch should not be scratched.

Clothing, towels and bedding should be washed on a hot cycle to avoid infecting others or yourself. As with crabs it is important that anybody who you think might have been infested at the same time as you, and with whom you are in intimate contact treats themselves at the same time as you to avoid reinfestation.

Crabs and scabies cannot pass on HIV. People with long-standing crab infestations can feel generally unwell (which is the origin of the term lousy) and if left untreated, scabies can cause severe skin irritation.

If you think you picked up crabs or scabies from sex, you should consider having a full sexual health check-up at a genitourinary medicine clinic to check for other infections.