The scalp/hair interface is very similar to the nail/cuticle interface in many respects. Here the nonliving hair abuts the living scalp, just like the nonliving nail abuts the living cuticle. The skin needs of the scalp are complex due to the presence of abundant sweat, sebum, and nerves all complicated by the presence of numerous hair follicles. It is beyond the scope of this text to deal with the many issues surrounding hair growth and cleansing, thus this section will focus strictly on the skin forming the scalp.
Anatomy and Physiology
It is important to recognize that healthy hair begins with a healthy scalp. The hair grows actually below the skin of the scalp with follicles protected in the subcutaneous fat covering the skull. The scalp has an abundant blood supply to provide the necessary nutrients for hair growth and an extensive nerve network. This is why injuries to the scalp bleed profusely and are quite painful. In addition to blood vessels and nerves, the scalp also has numerous eccrine sweat glands and sebaceous glands. These secretions provide nutrients for bacteria and fungus that can infect the skin of the scalp. The hair also increases the chances for infection by providing abundant surface area for organisms to grow. Lastly, sweat can function as an irritant, accounting for the frequent itching associated with areas of sweat collection, such as the nape of the neck. The presence of the neural network around the hairs also provides more opportunities for sensation of itch to be induced.
Common Dermatologic Disease Considerations
The scalp is the site of many dermatologic diseases, the most common of which is dandruff. Dandruff lies on a spectrum between occasional mild flaking of the scalp to thick oozing plaques devoid of hair, known as seborrheic dermatitis. Both of the conditions are caused by the same fungal organism named Malassezia globosa. This fungal organism is present in the air and lands on the scalp rich in sebum. It consumes the sebum and leaves behind free fatty acids that are extremely irritating to the scalp skin. These free fatty acids induce itching, inflammation, and increase the scalp skin turnover resulting in flaking. If the immune system is intact, the body will not allow the Malassezia to proliferate and the skin remains healthy. If the immune system is not intact, such as with advancing age, the presence of illness, or human immunodeficiency virus (HIV) infection, the Malassezia organisms will multiply and their sheer number will induce an infection. A mild infection may be perceived as dandruff, but a more severe infection is termed seborrheic dermatitis. The key to preventing a Malassezia
scalp infection is the use of topical antifungals in the form of shampoos containing zinc pyrithione or selenium sulfide or ketoconazole. Active infection can be treated with prescription oral and/or topical antifungals.
It should be mentioned that other fungal organisms, besides Malassezia, could also infect the scalp. These include the same fungal organisms that cause athlete’s foot (tinea pedis) and nail fungal infections (tinea unguinum). Fungal infections of the scalp, medically known as tinea capitas, are commonly termed ringworm. A worm is not involved, but the areas of hair loss are round, hence the early misnomer that a round worm was causing the problem. The organisms that cause scalp fungal infections can be transmitted person to person on combs or through direct contact. For this reason, tinea capitas is mainly seen in children. It is a highly contagious infection requiring the use of oral prescription antifungal medication for eradication.
Bacteria can also affect the scalp creating an infection known as folliculitis. In this condition, the bacteria enter the scalp at the site where the hair exits the scalp, known as the follicular ostia. This is the weakest point of the scalp to infection, since the hair slightly tents the scalp, allowing this skin to sit above the rest of the scalp. When the scalp is scratched, the skin around the hair is preferentially injured and bacteria from beneath the fingernail placed in the scalp skin causes infection. As might be expected, folliculitis is a common complication of an itchy scalp. Folliculitis is usually treated with shampooing for good scalp hygiene, treatment of the scalp itch with topical corticosteroids, and oral antibiotics for the scalp bacterial infection. Shampoos and scalp products that prevent itch are important for maintenance therapy, since an itchy scalp is usually the initiating factor for scalp folliculitis.
Lastly, no discussion of scalp skin could be complete without the mention of psoriasis. As in all other body areas, psoriasis of the scalp is due to the production of too much poor quality skin too quickly. It presents with severe thick silvery plaques of scalp scale that may interfere with hair growth. It is best treated medically; however, shampoos and scalp solutions containing keratolytics, such as salicylic acid, or antiinflammatories, such as tar derivatives, are helpful. Antidandruff preparations, as discussed previously, may be helpful since the presence of Malassezia my initiate a flare of scalp psoriasis.
Hygiene Needs
The hygiene of the scalp must be maintained while beautifying the hair, which can be a cosmetic challenge. Cleanliness of the scalp is very important to prevent fungal and bacterial infection that can induce subclinical and clinical disease, without overdrying the nonliving hair. It is interesting to note that shaving the hair, which provides a ready surface for infection, can cure many scalp diseases. Certainly, this is not an alternative that would be considered by many!
Skin Care Needs
The skin care needs of the scalp are to remove excess skin scale, loosen shedding hair, and maintain the biofilm of sweat, sebum, and organisms in balance. Many might suggest that the scalp should be moisturized to smooth down the skin scale and allow barrier repair to occur. While this is generally the case in other body areas, this logic does not pertain to the scalp. Skin scale provides a home for the fungal and bacterial organisms and allows sweat and sebum to accumulate on the scalp. Removal of the skin scale is key to scalp skin health.