The term “scalp” refers to the skin on the top of the head. Like the skin that covers the other parts of the body, the scalp is also prone to getting infected. In fact, the skin of the scalp has a higher likelihood of getting infected than the skin present in other parts of the body. The factors that contribute to the susceptibility of scalp to infections include the presence of overactive sebaceous or oil glands, unwashed hair that trap environmental dirt, perspiration that gets trapped within the hair, and harsh hair treatments people do for cosmetic reasons.
The most common infections of the scalp are caused by bacteria and fungi. In addition, viruses can also cause scalp infections. Despite their common occurrence, scalp infections are superficial infections that do not pose any significant threat to the overall health of an individual. The adverse effects of scalp infections include formation of sores on the head and hair loss. These cosmetic effects do have psychosocial repercussions for the infected individual.
Read more on scalp problems.
Causes of Scalp Infections
The skin is the primary physical barrier that prevents infectious agents from entering the body. However, the skin itself harbors a variety of bacteria, fungi and viruses. These pathogens are usually kept in check by the activity of the immune system. Any break in the continuity of the skin or impairment of the immune system allows these pathogens to gain an upper hand and cause infections.
The following are some of the factors that predispose a person to get scalp infections:
- A weak immune system can allow pathogens to establish a scalp infection easily. People suffering from HIV/AIDS or poorly managed diabetes have a weakened immune system that makes them susceptible to a variety of infections, including scalp infections.
- People can get scalp infections by coming in close contact with other infected people or pets.
- Microbes can also be transmitted via sharing of inanimate personal objects such as combs.
Pre-existing conditions of the scalp, such as acne, psoriasis, and seborrheic dermatitis can increase the chances of getting scalp infections.
- Scratching the scalp excessively due to skin irritation can also increase the chances of skin infection.
- Irritation of the scalp can occur due to poor hygiene, accumulation of sweat, cosmetic hair extensions and nervous itching.
- Allergic reactions to hair straightening chemicals, hair dyes and shampoos can also lead to itching of the scalp.
- Chronic use of oral antibiotics and corticosteroid creams can also predispose an individual to scalp infections.
- Chemical, mechanical, and electromagnetic injury to the scalp can increase the likelihood of infections.
Types of Scalp Infections
Scalp infections can be classified on the basis of the causative infectious agents. The main pathogens responsible for scalp infections are bacteria, fungi, and viruses. However, there may be other causes, such as parasites like mites and head lice.
Fungal scalp infections
Fungi are one of the most common causes of skin infections, including scalp infections. Not all fungi cause skin infection though. Overgrowth of fungi on the skin or immune reaction to the presence of fungi on the skin can cause skin inflammation.
Two types of fungi cause skin infections in humans – yeasts and dermatophytes. Yeasts are single cell organisms that usually cause infections of body cavities such as the vagina and the mouth. They can cause opportunistic skin infections as well.
Dermatophytes, on the other hand, primarily cause skin infections. Dermatophytes have a predilection for the skin. Specialized enzymes present in dermatophytes are able to digest the keratin protein present in the skin, enabling them to live on the skin.
The following are examples of fungal scalp infections caused by dermatophytes and yeasts.
- Tinea capitis: Tinea capitis is one of the most common fungal infections of the scalp. A variety of dermatophyte species can cause tinea capitis. A characteristic feature of tinea capitis is the formation of a ring-like rash on the skin. Due to this feature, tinea capitis is also sometimes referred to as scalp ringworm. The infected skin in tinea capitis is usually quite itchy. Pus-filled bumps (known as kerions) may also be present in the infected skin areas. Tinea capitis can lead to hair loss.
- Yeast infection: Yeasts belonging to the genus, Malassezia, are found to occur naturally on the human skin. Under normal conditions, Malassezia yeasts do not cause skin infections. However, these yeasts can cause opportunistic infections under certain conditions. Examples of scalp infections caused by yeasts include seborrheic dermatitis and folliculitis. Non-infectious skin conditions such as scalp psoriasis may also be exacerbated by Malassezia infection.
Bacterial scalp infections
Bacteria are present everywhere in the environment. They are also the most common microbes found on and inside the human body. A number of bacteria are a part of the normal flora on the human skin. Some of these bacteria are harmless, whereas others can cause serious infections and diseases.
Even harmless bacteria on the skin can cause diseases when they get an opportunity via breaks in the skin or a weakened immune system. Bacterial infections that penetrate beyond the superficial skin layer can even become life-threatening.
The following are a couple of examples of bacterial scalp infections:
- Folliculitis: An infection of the hair follicles is referred to as folliculitis. It is possible for a healthy scalp can get folliculitis. However, folliculitis is more likely to occur when there is a blockage of hair follicles or injury to the hair follicles. Although folliculitis can be caused by a number of different microbes, bacteria remain the most common cause. Among bacteria, Staphylococcus aureus and Propionibacterium acnes are most commonly responsible for folliculitis of the scalp. Other organisms that can cause folliculitis include viruses, fungi and mites. Scalp acne may also exist alongside scalp folliculitis.
- Scalp impetigo: Impetigo is a superficial skin infection caused by bacteria. The most common causes of impetigo are infections with the Staphylococcus aureus and Streptococcus pyogenes bacteria. Impetigo of the scalp is not a common condition. It usually occurs as a secondary infection after the scalp has been battered with fungal infections, skin diseases, or head lice infestations. When the superficial bacterial skin infection manages to penetrate into the deeper tissues, the condition is referred to as cellulitis.
Read more on scalp acne.
Viral skin infections
Scalp infections caused by viruses are not very common. In most cases, viral scalp infections are a manifestation of some systemic viral infection. The following are some examples of viruses that can cause infections of the scalp:
- Chickenpox virus: Scalp lesions are common in chickenpox infection, especially in children. In chickenpox, tiny blisters appear on the skin all over the body. Reactivation of chickenpox virus (Varicella zoster) in the body is also responsible for the extremely painful skin condition known as shingles. Scalp may also be affected in shingles.
- Herpes simplex virus: Herpes simplex virus (commonly abbreviated as HSV) that causes facial cold sores may also be responsible for scalp folliculitis.