Several types of lice, bacteria, and fungi can invade the scalp and cause numerous problems. These infectious agents of the scalp and other regions of hair are collectively called "dermatophytes". Different dermatophytes are common in different parts of the world and at different times in history. The same clinical diagnosis today may be caused by something very different than the same clinical diagnosis fifty years ago. For example the most common cause of tinea capitis in Europe and the USA in 1955 was Microsporum audouini. Today the most common cause of tinea capitis may be due to other infectious agents such as Trichophyton tonsurans and Microsporum canis in Europe.

Scalp infections and infestations are still very common today, even in the developed Western world. Because the diseases are due to bacteria, fungi, viruses, and microscopic animals, they can easily be transmitted from one individual to another. Transmission usually occurs between those living in close proximity to each other where there may be physical contact. However, it is also possible to transmit infectious scalp agents through using contaminated towels, from contact with infected animals including pets, or even from contact with contaminated soil or water. “Hot Tub” Folliculitis is a condition caused by the pathogen Pseudomonas Aeruginosa, and is often seen where spa and public bath sanitation is at fault. Public hot tubs are a particularly common source of infection, as they are nice and warm, but often not very clean, so the bacteria can survive and as so many people use them cross infection is easy.

Infectious diseases of the hair follicle may be caused by bacteria, fungi, viruses or parasites, but the most common skin pathogens that cause infectious skin and hair diseases are bacteria or fungi. In bacterial infections, Staphylococcus aureus and a group of bacteria called Hemolytic Streptococci are particularly common. The pathogens identified in Gram-negative folliculitis include Klebsiella, Enterobacter, and Proteus species. The type of fungus in fungal infections varies signficantly.

Viral infections of hair follicles are relatively rare and where it does occur it is almost always caused by Herpes Simplex. Mites such as Demodex folliculorum and Demodex brevis are natural and common parasites of the human pilo-sebaceous follicle. Usually they live a benign life and promote nothing more than a mild itch (if you have itchy eyelids it is most likely a Demodex infestation that is causing it). However, occasionally Demodex species can sometimes induce a stronger inflammatory reaction and folliculitis is the result. A yeast induced folliculitis is quite rare, but Pityrosporum folliculitis is caused by pityrosporum yeasts and very rarely Candida albicans can cause folliculitis in immunocompromised individuals.

Because there can be such a wide variety of infectious pathogens that can cause folliculitis or worse, a careful evaluation of the condition is important to ensure the most appropriate treatment is provided.

This section of the web site examines different forms of hair follicle infection or skin infection that can affect adjacent hair follicles.