Common infectious hair diseases Scalp infections and infestations are still very Common infectious hair diseases today, all over the world. Common infectious diseases of hair are caused either by fungus, bacteria, viruses or parasites 01. Piedra is a major fungal infection 02 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 Folliculitis on the scalp. Bacterial folliculitis can be both superficial and deep 03. 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 a parasite called Demodex folliculorum 04\u00a0causes major itching and infection in people suffering from pattern baldness. Cause of Common infectious hair diseases People have a misconception that this parasite causes alopecia 05 by infecting the hair follicles. But this belief has been proved wrong by the current experimental studies. Quite recently it has been suggesting that Demodex folliculorum infection is a consequence of pattern baldness. It is not the cause of alopecia. 1- Demodex folliculorum parasite Demodex parasitic infection of hair follicles is one of the common infectious diseases that affect 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 06. 1.1 - Role of the parasite The Demodex parasite\u00a0feeds 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) 07. The oils combine with dead cells of the affected hair follicle to make sebum 08. 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 09. 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 11. 1.2 - Effects Demodex folliculorum infection is one of the common infectious diseases different between men and women. The major problem with the Demodex parasite is it may cause irritation, particularly if the infection is in the eyelashes 12. It is believed that the frequency of Demodex folliculorum infection is less in children. It is a common infectious hair disease that's 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. 1.3 - Treatments The most widely available treatment for this parasitic infection is pilocarpine gel. However, the application of this remedy does not promote any hair growth in pattern baldness. 2 - Piedra The visible indicator of Piedra (Trichomycosis Nodularis 13) most common infectious hair diseases 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 14. There are two varieties of Piedra 15 \tBlack Piedra \tWhite Piedra. 2.1 - Black Piedra Black Piedra is due to the fungus Piedra hortae and Trichosporon Ovoids 16. It is mostly found in tropical countries like South America and Southeast Asia. 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. 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 the 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. 2.2 - White Piedra In contrast, White Piedra is due to the fungus Trichosporon beigelii 17 and is found mostly in Europe and Southern parts of the USA. 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. 2.3 - Effects 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. 2.4 - Treatment Treatment of Piedra generally involves shaving off the hair in the affected area. Common products used to treat piedra are shampoos formulated with salicylic 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 that can cause various common infectious diseases like folliculitis, tinea capitis, or seborrheic dermatitis, a careful diagnosis of the condition is important to ensure the most appropriate effective treatment is used.