Some common ones are described here:
Folliculitis
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.
Piedra
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.
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 it's 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.
Ringworm
Surprisingly, ringworm has nothing to do with worms, but is a fungal infection that can occur anywhere on the body.
If it develops on the scalp, it can cause patches of hair loss and is known to doctors as "tinea capitis."
Ringworm is the same thing as athlete's foot, and the same kind of fungal infection that can affect the nails too.
On the scalp, ringworm usually begins as a small pimple that progressively expands in size, leaving scaly patches of temporary baldness.
The fungus gets into the hair fibers in the affected area and these hairs become brittle and break off easily, leaving a bald patch of skin.
Affected areas are often itchy, red, and inflamed, with scaly patches that may blister and ooze.
The patches are usually redder around the outside with a more normal skin tone in the center.
This may create the appearance of a ring, hence the name, ringworm.
