Hair Disease

Common infectious hair diseases

Some common infectious diseases

Scalp infections and infestations are still very common today, all over the world. Common infectious diseases of hair are caused either by fungus, bacteria, viruses or parasites.

Piedra is a major fungal infection which affects a majority of ethnic groups, but its infection is restricted only to particular regions of the world. Some common infectious diseases of hair are caused by bacteria. It can induce Folliculitus on the scalp. Bacterial folliculitus can be both superficial and deep. Superficial folliculitis may cause only temporary hair loss but deep seated folliculitis heals slowly and often leads to scarring and permanent hair loss. Apart from bacteria and fungi a particular species of parasite called Demodex folliclorum causes major itching and infection in people suffering from pattern baldness.

People have a misconception that this parasite causes alopecia by infecting the hair follicles. But this belief has been proved wrong by the current experimental studies. Quite recently it has been suggested that Demodex folliculorum infection is a consequence of pattern baldness. It is not the cause of alopecia.

Demodex folliclorum parasite

Demodex parasitic infection of hair follicles is one of the common infectious diseases that affects the scalp. It can infect any hair follicle but it particularly prefers face and scalp hair follicles. Individuals affected by acne or seborrhea oleosa are more prone to be attacked by this particular parasite.

Role of the parasite

The demodex parasite feeds on dead skin and oils, so it particularly likes to live in hair follicles where there are lots of both and that usually means the follicles of the face and scalp. Oil is produced in a large amount in pattern baldness under the influence of dihydrotestosterone (DHT).

The oils combine with dead cells of the affected hair follicle to make sebum. The sebum provides a rich source of nutrients for the Demodex folliculorum parasite. In general, the oil food supply to the parasite increases the severity of pattern baldness.

The affected hair follicles in pattern baldness can accommodate a large number of Demodex Folliculorum parasites. While they are sometimes found on the surface of the skin, they are more commonly encountered in the sebum substance of hair follicles called comedo plugs or blackheads. A comedo plug is situated under the skin surface in the canal of the hair follicle where the hair fiber grows. It is composed of keratin and sebum and is blackened at the surface. About five to twenty demodex parasites can be situated in the comedo plug of a single hair follicle.


Demodex folliculorum infection is one of the common infectious diseases found in men and women. The major problem with Demodex parasite is they may cause irritation, particularly if the infection is in the eyelashes.

It is believed that the frequency of Demodex folliculorum infection is less in children. It is rarely found in children who are below 5 years old. While between the age group of 5 to 10 years, it is found in around 50% and in between the age group of 10-20 the percentage is same as in adults (around 75%). It is impossible to consciously avoid the parasitic infection without the help of medications.


The most widely available treatment for this parasitic infection is pilocarpine gel. However, application of this remedy does not promote any hair growth in pattern baldness.


The visible indicator of Piedra (Trichomycosis Nodularis) infection is the development of hard nodules on hair fibers. The source of infection and method of transmission is unknown but it is suggested that the fungus is transmitted from person-to-person. Both the genders and people of all ages are equally affected by this common infectious disease.

There are two varieties of piedra:

  • Black piedra
  • White piedra.

Black Piedra is due to the fungus Piedra hortae and Trichosporon ovoides. It is mostly found in tropical countries like South America and South East Asia.

In contrast, white piedra is due to the fungus Trichosporon beigelii and is found mostly in Europe and Southern parts of the USA.

It has been suggested that in some ethnic groups, black piedra may have cosmetic importance. Traditionally, women of several South Pacific islands slept with their hair buried in soil. They actually encouraged the infection and development of black piedra. The nodular concretions of the fungal infection were regarded by some traditional societies as quite attractive.


This common infectious disease may affect hairs of the scalp, body and genital areas. However, when the infection is severe the fungus weakens the hair fiber making it easy to break off. Also it can result in patchy hair loss.

Black piedra is a condition which more commonly affects black African-Americans compared to other ethnic groupings. It is characterized by the presence of firm black, hard, gritty nodules, which are actually a mass of fungus cells on the hair shaft. They cause disintegration and breakage in the hair fiber. In general, black piedra is more frequent than white piedra. Sometimes the tiny nodules of black piedra can be recognized by a metallic sound when the hair is brushed.

White piedra in hair fiber consists of lightly pigmented, loosely attached nodules on a soft hair shaft. The most commonly affected areas of the body are beards, mustaches, pubic and axillary hair, along with eyelashes and eyebrows.


Treatment of Peidra generally involves shaving off the hair in the affected area. Common products used to treat peidra are shampoos formulated with salycylic acid. However, these shampoo formulas have been recently superseded by azole based shampoos. Azole antifungals, are probably the best treatment for black piedra currently available. Oral therapy with either ketoconazole or terbinafine is also a major hair care product for this fungal infection.

As there are a wide variety of infectious micro-organisms which can cause various common infectious diseases like folliculitis, tinea capitis or sebhorriec dermatitis, a careful diagnosis of the condition is important to ensure the most appropriate effective treatment is used.