STD parasites are small bugs that either live on or under the skin. Some parasites also live in the wet, warm areas of the body like the genitals. They are extremely common and very easy to spread through intimate contact like sex, but some of them can also be spread through contact with things like bedding.

These STDs are generally more annoying than harmful and can be a challenge to treat. The important thing to remember is that people who get a parasite STD are at more risk of getting one of the more serious STDs.

Pubic Lice (“crabs”)

Pubic lice are small insects found in the genital area of humans. They are common and found everywhere in the world. Pubic lice are usually spread through sexual contact. They are sometimes spread through contact with bedding, towels or clothing used recently by someone who has pubic lice. It is not possible to get them by sitting on a toilet seat.

Signs and Symptoms

Most people have intense itching, but not everyone. Some people can see the lice and the eggs which are attached to pubic hairs. You may notice small blue spots on your skin or tiny blood spots in your underwear as a result of their bites.

Testing for Pubic Lice

Adult lice are large enough to see with the naked eye, so a doctor’s diagnosis is not usually necessary. However, people who get pubic lice should be tested for other STDs.


There are shampoos, rinses and lotions that are designed to kill pubic lice. You can buy them in most drugstores. The directions on the package should be followed very carefully. Some products cannot be used by pregnant women or very young children. If there are lice in the eyebrows or lashes, use a product specially made for that purpose.

Washable clothing and bedding should be washed in hot water and dried in a hot dryer. Dry clean other items that cannot be washed. Things that cannot be dry cleaned or washed can be sealed in a plastic bag for 10 days so that the lice and lice eggs die.

It’s important that everyone you have had sex with in the last month be treated also or you will get lice from them again.


Scabies is a skin infestation caused by tiny bugs called mites. They are common and found everywhere in the world. Scabies is spread through direct skin-to-skin contact and is easily passed between sexual partners and close household members. The mites live under the skin in the moist folds of the body, especially between the fingers and toes. They also live in the genital areas, under the breasts and armpits.

Signs and Symptoms

They are too small to be seen without a microscope, but the mites cause intense itching and rashes. Small pimple- like spots may be present as well.

Testing for Scabies

Scabies is most commonly diagnosed by looking at the rash. The doctor may take tiny scrapes of skin to look at under a microscope.


There are special lotions that kill the mites and their eggs—follow directions carefully. Pregnant women and very young children should not use some kinds of scabies lotions. Talk to your doctor about what’s safe. Itching may continue for 2–3 weeks after treatment.

Clothing, bedding and other linens that can be washed should go in the hot cycles for both washers and dryers. Items that cannot be put in hot water can be either dry cleaned or sealed in a plastic bag for 3–4 weeks. Everyone you have had close contact with should be treated at the same time.

Trichomoniasis (“trich” or trichomonas vaginalis)

This common infection is caused by tiny parasites called protozoa. They live in wet areas of the genitals, such as the urethra or vagina. While it is most commonly passed from one person to the next during sex, it can sometimes be spread through genital contact with wet towels, wet toilet seats or wet clothing.

Trich doesn’t cause any lasting damage for adults but it can cause pregnant women to have premature or low birth-weight babies.

Signs and Symptoms

Trich causes inflammation. In women, it can cause vaginitis (inflammation in the vagina) and in men it can cause urethritis (inflammation in the urethra).

Like many STDs, people don’t always have symptoms. If there are symptoms, they usually appear 5–28 days after sex. But symptoms can also appear months or even years later. They can pass the infection on to others even if they have no symptoms.

Only about half of women with trich have symptoms. They may have any or all of the following symptoms: yellow, green or gray vaginal discharge (often foamy) with a strong odor and pain during sex or urinating. There may be irritation and itching. The irritation can make it easier to get another STD infection.

Most men have no symptoms. They may have clear or white discharge from the penis or sometimes burning with ejaculation or urination.

Testing for Trich

The doctor will use a swab to take fluid from the vagina or penis and look for the protozoa under a microscope. A better test is a culture but it takes longer and is more expensive. Trich can also be found in the cells taken for a Pap test, and male semen can be checked.


The doctor will prescribe an antibiotic. Be sure to tell your doctor if you are pregnant, because some of the medicines should not be used by pregnant women. It’s important not to have sex until you are finished with medicine. All partners should be treated also. If all partners are not treated at the same time, you can get trich again.