Some infectious agents and infection-related conditions can contribute to hair loss as well as the loss of body hair.
The most common are:
- ringworm of the scalp also known as tinea capitis – a fungal infection that causes itchy, red and inflamed patches of hair loss that gives an appearance of the ring.
- folliculitis-an inflammation of hair follicles that when severe can permanently destroy hair follicles. There are two groups of this condition: non-infectious (caused by oils and grease that clog up the hair follicles) and infectious (e.g.caused by Staphylococcus aureus and Pseudomonas aeruginosa).
- seborrheic dermatitis– a very common skin condition and when located on the scalp it can involve temporary hair loss. Sebaceous glands attached to the hair follicles produce a very rich form of sebum resulting in a scaly appearance of the scalp. It might be caused by elevated androgen steroids.
- lichen planus and lichen planopilaris– an inflammatory autoimmune condition that causes white blood cells to attack healthy skin, and when bumps appear on the scalp it may lead to permanent hair loss.
- lichen simplex-a skin condition that causes chronic itching. If the hair follicles on the scalp become irritated from the itching and raw areas associated with lichen simplex, hair loss may occur.
- psoriasis – a common, auto-immune, non-contagious skin condition that runs in families, where multiple raised, reddish and scaly patches appear on the skin. Severe cases of psoriasis may cause temporary hair loss, but the hair grows back once the condition has been treated and is under control.
- demodex folliculorum– a little worm-like mite that lives in hair follicles and feeds on dead skin and the sebum produced by sebaceous glands. About 70% of adults have some Demodex in their hair follicles, particularly in an oily scalp environment. The most common problem with Demodex is that they may cause irritation that leads to hair loss, particularly in the eyelashes.
- syphilis – a sexually transmitted infection that can be acquired or congenital and has four stages with various symptoms. It can also create non-specific, patchy hair loss in the scalp, eyebrows and eyelashes.