Folliculitis is an inflammation or infection of the hair follicles. It's caused by bacteria (usually staphylococcus bacteria) that find their way into the hair follicles from a nearby infection. The follicles also can become irritated from shaving or wearing certain types of makeup or irritating clothing. Some people develop folliculitis after taking a dip in a hot tub. This condition is referred to as "hot-tub folliculitis."
Folliculitis looks like small, pus-filled pimples at the base of each hair. Some mild cases will go away without treatment, but an antibiotic can help clear up the bacteria and relieve the condition more quickly. If the infection is caused by irritation from shaving, waxing, or plucking the hair, you might need to hold off on these activities for a few weeks to allow healthy hair to grow in.
Psoriasis is a skin condition that can affect the skin just about anywhere on the body, including the knees and elbows, but it's often found on the scalp. It causes the body to make too many new skin cells, leaving an excess of skin cells on the scalp. The excess cells can form thick, crusted scales and make the scalp feel itchy or sore.
Psoriasis is usually treated with steroid creams or ointments. Shampoos containing tar or salicylic acid may also be helpful. Ultraviolet light therapy may also help some people with psoriasis. Severe forms of psoriasis may require treatment with an injected medication.
Lichen planus is a skin disease that can affect the skin or mouth. No one knows for sure what causes it, but there are a number of theories, ranging from stress to genetics. It may also be connected to the hepatitis C virus, so if you have lichen planus you might need to be tested for hepatitis too. Lichen planus is believed to be an autoimmune disease, which means that the immune system mistakenly attacks your own body. Medications used to treat high blood pressure, heart disease, and arthritis can sometimes cause a lichen planus-like irritation.
People who have lichen planus develop flat-topped, purple or reddish bumps on their skin. These bumps can be very itchy. Lichen planus can lead to redness, irritation, and hair loss on the scalp (which can be permanent). Although the bumps will eventually go away on their own, treatment can relieve the symptoms and help the rash clear up more quickly. The main treatment is with steroid medications that are either rubbed on the rash, injected, or taken by mouth. Retinoid medications used for acne may also be used. Antihistamines (such as Benadryl) or soothing baths can often help relieve itching. Sometimes a type of ultraviolet light therapy (PUVA) is used as part of treatment.