Folliculitis is a term for inflammation of hair follicles. It looks like acne with little rings of inflammation surrounding the opening of a hair follicle. In the early stages of a folliculitis, the hair fiber may still be present, but as the folliculitis progresses the hair often falls out. When folliculitis is severe, inflammation is so intense that it can permanently destroy the hair follicles, leaving little bald patches.
There are non-infectious forms of folliculitis, such as those caused by oils and greases applied to the skin that clog up the hair follicles, but folliculitis is usually due to a bacterial infection. Particularly common is an infection of the hair follicles by Staphylococcus aureus. "Hot tub folliculitis" is caused by Pseudomonas aeruginosa which grows in inadequately chlorinated water.
Nonprescription topical antibiotics such as bacitracin, mycitracin, or neomycin can be used to treat minor folliculitis. For more serious infections, oral antibiotics such as erythromycin may be used.
Piedra (trichomycosis nodularis) happens when the hair fibers are infected by a fungus. The visible indicator of a piedra infection is development of hard nodules on hair fibers. Indeed, "piedra" is Spanish for stone. The nodules are a concretion of hyphae and fruiting bodies of the fungus, known as an ascostroma, from which the fungal spores are released.
There are two basic types of piedra: black piedra and white piedra, referring to the color of the nodules formed on the hair fiber. Black piedra is due to the fungus Piedraia hortae and is mostly found in tropical countries, while white piedra is due to Trichosporon beigelii and is found mostly in Europe and Southern parts of the United States.
Piedra infection may affect hairs of the scalp, body, and genital areas. Usually the infection is relatively benign. In parts of Malaysia, the nodules of black piedra are considered attractive and traditionally women encouraged its growth by sleeping with their hair buried in the soil. However, when the infection is severe the fungus weakens the hair fiber, making it easy to break off. This can result in a patchy, diffuse hair loss.
Treatment generally involves shaving off affected areas. Anti-fungals such as ketoconazole or terbinafine are also used.