Fungi on the Skin
There are various types of skin infections caused by fungi (singular ~ fungus). The most common of these are dermatophytes (tinea) and yeasts. Another group known as molds are often discussed in conjunction with dermatophytes because an infection causes a similar appearance on the skin and may co-exist and complicate a dermatophyte infection. However, molds are different from dermatophytes. Most of us know of the common skin infections on the feet (athlete’s foot) and groin (jock itch). These are dermatophytes or tinea, often referred to as ringworm. It is named according to the site that is affected – tinea pedis (tinea of the foot or athlete’s foot) or tinea cruris (tinea of the groin or jock itch). Yeasts are a different subtype of fungi from dermatophytes. The common species of yeasts that we hear of are Candida and Malassezia. Yeasts can also infect the skin but the presentation may be slightly different from infection with dermatophytes. Due to this difference in presentation and subtype of fungus, yeast infections of the skin or scalp are termed pityriasis. The exception is with tinea versicolor. (1)
What is tinea versicolor?
Tinea versicolor is an yeast fungal infection of the superficial layers of the skin most commonly affecting the neck, upper arm, chest and back. The term tinea suggests a dermatophyte infection but tinea versicolor is actually due to an yeast. Therefore the correct term for this type of fungal infection of the skin is pityriasis versicolor. It mainly occurs on the neck, chest, back and upper arms and rarely extends to other areas. Fungal infections on the skin of the face are more commonly due to dermatophytes, not yeasts, and are more correctly referred to as tinea faciei. However, most people still refer to pityriasis versicolor as tinea versicolor and consider superficial fungal infections on the face to be within this condition. Overall tinea versicolor is a common cinfection and more frequently seen in hot and humid regions where it can affect as much as 50% of the population. In the United States, it is believed that the incidence is about 2% to 8%. (2)
Tinea Versicolor Causes
Tinea versicolor is caused by a group of yeasts known as Malassezia. This group was previously known as Pityrosporum, hence the term pityriasis. There are several different types of Malassezia yeasts but the most common ones responsible for tineas versicolora are Malassezia furfur and Malassezia globosa. Unlike other infections which are acquired when the microorganisms are introduced to the body, these yeasts naturally occur on the skin and do not cause any disease in most cases. It is known as the normal skin flora along with other yeasts and various species of bacteria. However, under certain conditions these microorganisms can turn pathogenic – meaning that it can cause disease.
The yeast on the skin exists both in an inactive form known as spores and active filamentous form. It can feed on dead skin cells and is known as a saprophyte. Normally there are various factors that control and limit the population of the yeast on the skin surface. The main factors are the integrity of the skin, the body’s defenses and the presence of other microorganisms on the skin that make up the normal flora. For some reason that has not been conclusively identified in every cases, there is an overgrowth of this yeast. More spores germinate allowing it to take on an active form. It causes the typical rash on the skin seen with a fungal infection. The yeast therefore changes from being a saprophyte to a parasite.
Although the cause for the overgrowth is not always known, there are several risk factors that have been identified.
- Living in hot and humid environments
- Impaired immune defenses
- Poor nutrition
- Diseases like Cushing’s disease
- Hormonal changes
- Excessive perspiration (hyperhidrosis)
- Oily skin
Tinea Versicolor Symptoms
The term pityriasis versicolor probably best describes what the rash looks like. Pityriasis = scales. Versicolor = multi-colored. The rash appears as patches of oval to round lesions of dry skin. The color of these patches vary from pink to to darker or lighter brown than the surrounding skin. Pale patches are more frequently seen in darker skinned individuals and is sometimes mistaken for conditions such as vitilio. However, tinea versicolor is not vitiligo. In some cases, the patches of dry skin may at first appear darker than the surrounding skin and then become paler to almost white in color.
|Pictures above are typical of tinea versicolor rash. Courtesy of Samuel Freire da Silva, M.D. (www.atlasdermatologico.com.br)|
The patches grow very slowly and are more like “islands” dotted on the normal skin. It can coalesce into large patches over time. Tinea versicolor is mildly itchy and tends to become more prominent after sun exposure. This does not mean that tinea versicolor is more likely to occur on sun exposed areas. In fact it is almost always seen on the back, upper arms, chest and sometimes extending to the neck. The sun exposed areas like the face and forearms are usually spared although other dermatophyte infections may be seen on these areas.
Tinea Versicolor Pictures
Tinea versicolor may be present in one of four forms. The presentation may seem uncharacteristic of the typical presentation and can lead to confusion. It may even appear on areas such as the face, elbows and abdomen. This, however, is uncommon and more likely to occur in a person who has a weakened immune system.
Tinea versicolor back
|Pictures above are of tinea versicolor on the back. Courtesy of Samuel Freire da Silva, M.D. (www.atlasdermatologico.com.br)|
Tinea versicolor arms
Tinea versicolor chest
|Pictures above are of tinea versicolor on the chest. Courtesy of Samuel Freire da Silva, M.D. (www.atlasdermatologico.com.br)|
Tinea versicolor diagnosis
The diagnosis of tinea versicolor can be made on clinical examination. The typical appearance combined with other factors such as its distribution and reaction to sunlight. Other methods of diagnosing tinea versicolor includes :
- Microscopic examination of skin scrapings on a potassium hydroxide wet mount.
- Wood lamp’s examination where the affect skin fluoresces yellow-white to golden-white.
Tinea versicolor treatment
Tinea versicolor can be treated with topical or oral antifungals. Treatment usually lasts for about a month. The skin color should return to normal within one to two months. Tinea versicolor may recur after treatment.
Topical applications are applied on the skin in the form of solutions, creams, lotions and ointments. This includes :
- Selenium sulfide
- Sodium thiosulfate
- Ketoconazole or other topical azoles
Oral antifungal agents are in the form of tablets or capsules. Infection tends not to recur for several months after using oral agents but it is not a permanent preventative measure. Commonly used oral agents includes :
1. Pityriasis versicolor. Dermnet NZ
2. Tinea versicolor. Emedicine Medscape