Skin fungi cause infections on the skin, hair and nails. They draw their nourishment from keratin. This is a main component of keratinized skin, hair and nails. The inflammation occurs as a defense reaction of the immune system to the foreign organism.
Major fungi are not capable of penetrating deeper into an immune-active host. Therefore, dermatomycosis is usually limited to the non-living part of the outer skin layer (epidermis).
The host's reaction to the foreign organism can vary from mild to severe. The course of the inflammation depends on the individual
- the specific skin fungus and
- the reaction of the immune system or
- the success of the medical therapy.
Some of the inflammations caused by fungal skin infections are also known as ringworm or tinea.
Every third German has to contend with a skin fungus from time to time. Athlete's foot is by far the most widespread and is therefore also one of the most common skin diseases. Athlete's foot is transmitted from person to person or from an animal.
The risk of dermatomycosis increases with poor hygienic conditions.
Dermatophytes are different types of filamentous fungi. They generally only cause infections of the skin. These skin infections are then called dermatophytoses (or more generally: dermatomycoses).
The word part "dermato-" refers to "dermis", the skin. This word stem can also be found in the specialist term fordermatologists. In science, the suffix "-phyte" can also stand for plants. In microbiology, however, it is usually used for dermatophyte species.
Meanwhile, mycosis is always a parasitic fungal infection of living tissue. Depending on the localization of the fungal disease, one speaks of
The causative agents of fungal skin infections are mostly dermatophytes. The fungi almost exclusively infect keratinized areas of the body such as skin, nails or hair.
Microbiology distinguishes between three relevant genera of dermatophytes:
- Trichophyton,
- Microsporum and
- Epidermophyton.
A further classification into
- geophilic,
- zoophilic and
- anthropophilic dermatophytes
takes into account, among other things
- the habitat,
- the pathogen reservoir and
- the different chains of infection.
Geophilic dermatophytes live in the soil. Contamination occurs during gardening, for example, but this does not inevitably lead to infection. Only local predisposing factors such as
make it easier for the ubiquitous pathogen to start an infection.
Zoophilic dermatophytes live mainly on the fur of animals. They are transmitted through contact (e.g. a child cuddling a guinea pig). An example in rural areas is Trichophyton verrucosum, which causes "cattle lichen" in animals. Under good conditions, the fungus can also be transmitted to humans. Zoophilic dermatophytes also cause more severe inflammation in humans.
Antropophilic dermatophytes are adapted to humans. They can be transmitted from person to person, directly or via dead objects. They are very infectious, but have rather minor consequences of infection. The two "main suspects" from this area are
- Trichophyton rubrum (mainly affects the skin) and
- Trichophyton mentagrophytes (mainly affects hair).
Up to 90 percent of all fungal skin infections are caused by these two pathogens.
Dermatophytes thrive wherever it is moist, warm and dark. They therefore like to infest
- the feet, especially the spaces between the toes and
- skin folds, i.e. under the female breast, in the armpit or in the groin.
Athlete's foot" is therefore a very common disease. Athletes with sweaty feet in warm, tight shoes provide ideal growth conditions for dermatophytes.
In addition, athletes often use communal showers and spend time in changing rooms. The pathogen is transmitted either
- directly from skin to skin or
- via the floor of gyms, showers, saunas, etc.
The filamentous fungus Trichophyton tonsurans has probably immigrated to this country from the USA. It is often found in gymnasts and wrestlers - it is also known as the "sports mat fungus".
Otherwise, there are predisposing factors for any fungal skin infection:
- Diabetes mellitus weakens the body's defenses and thus also makes it susceptible to fungal skin infections.
- Peripheral arterial occlusive disease(PAD, "intermittent claudication") leads to circulatory disorders in the hands and feet. This makes it easier for pathogens to take hold.
Microsporum canis is being transmitted more and more frequently. Cats are the main reservoir of pathogens. Small children are usually affected. The fungus exploits their immune system, which is not yet fully functional. It prefers to infect the hair(tinea capitis).
Healthy skin can usually keep hostile organisms from penetrating. The top layer of skin consists of flat, dead cells. These dead cells form a protective layer over the other layers of skin.
Above this layer, the skin has an acid mantle, which is formed from skin oil and perspiration. This acid mantle provides a very hostile environment for many bacteria, viruses and fungi. When the acid mantle or skin layer becomes permeable, the skin becomes susceptible to invaders.
The most common fungal skin infections are:
Ringworm (Tinea corporis)
Ringworm, ringworm or tinea corporis are fungal skin infections that occur on
- legs,
- arms,
- upper body or
- face
are found. They cause itchy, ring-shaped rashes.
Pronounced tinea corporis around the armpit © RandomizeTH | AdobeStock
Athlete's foot (tinea pedis)
Tinea pedis is a specific type of skin fungus on the foot. This form of infection affects more men than women. The infection usually starts between the toes. This is where a lot of moisture accumulates, making the area particularly susceptible to infection.
The skin fungus can then spread to the sole of the foot.
Tinea cruris
Tinea cruris also affects the foot. The pathogens enter the organism via contaminated soil through an injury to the skin layer.
Tinea capitis
Tinea capitis is a special form of skin fungus. It attacks the hair roots and manifests itself in the form of black spots on the scalp.
Fungal infections are usually characterized by severe itching. Also
- redness,
- skin peeling,
- cracks or
- ring-shaped rash
can also occur. If the skin fungus affects the scalp or beard, hair loss may occur.
Infected nails become thick, discolored and can also become deformed. Very serious infections can lead to abscesses or cellulitis.
A medical history is taken at the beginning of the diagnosis. The doctor will ask about
- the location of the infestation,
- the place of residence,
- past travel destinations or
- contact with animals.
The ethnic background can also play a role.
Hyphal fungi can often be recognized directly as they leave a thread-like structure in the uppermost layer of the skin.
Trichophyton is the fungus that causes tinea capitis. It can be recognized by small dark incrustations at the hair roots.
For a complete identification of the skin fungus, it is necessary to observe a sample on a carrier medium. Fungal growth begins after 5 to 14 days. A laboratory examination of this medium is the most accurate way of identifying the skin fungus.
A special rapid test has been developed for the most common skin fungi. The infected skin area is rubbed with this test. A bacterial carrier medium is integrated into the test. At a constant room temperature, the skin fungus develops in the test and changes color accordingly. Further analysis under the microscope is therefore not necessary.
The primary aim of treating dermatomycosis is to eliminate the fungus from the affected areas. The infections are treated depending on their occurrence.
Whether the treatment is systemic or topical also depends on the skin fungus.
The first measures consist of educating the patient about dermatomycosis. This includes
- changing footwear,
- using powders to keep the feet dry,
- avoiding walking barefoot in public places and
- advice not to share clothing, towels, combs and other items close to the body.
Treatment of tinea capitis
The systematic use of antimycotics is the mainstay of treatment for fungal infections. The duration of treatment depends on the choice of agent and can range from 2 to 8 weeks. Safety aspects, costs and efficiency depend on the choice of drug.
Griseofulvin is the oldest oral agent. Newer agents are terbinafine and itraconazole. All three are very effective, first-class drugs, especially for use over shorter periods of time.
Analyses have shown that terbinafine is more effective in the treatment of tinea capitis caused by Trichophyton strains. The reverse is true for Microsporum strains.
Both ketoconazole and fluconazole have been studied in tinea capitis. Both agents have proven to be effective. They are therefore good alternatives if
- the patient has an intolerance to griseofulvin, terbinafine and itraconazole or
- cost factors play a role.
Ketoconazole and fluconazole are only used as second-line agents. They have a higher risk of side effects. Antifungal shampoos do not usually solve the problem of infestation. However, they are a good solution to stop the spread of the fungus.
Treatment of tinea faciale, tinea corporis, tinea cruris, or tinea pedis
These types of fungal skin infections are usually found in the uppermost layer of the skin. They therefore respond to local treatment. Research has not yet been able to prove any significant differences in the efficacy of the various locally applicable antifungal drugs. However, it appears that the allylamine group of drugs is preferable for local treatment.
Tinea pedis (athlete's foot) is usually difficult to eliminate. Athlete's foot can develop rapidly if an infection reservoir
- in the nail bed or
- in the thick skin layer of the footbed
becomes established. Regular disinfection of shoes or even replacement of footwear may be necessary. If the skin fungus also affects the soles of the feet, a local antifungal spray will help. It should be applied over the entire surface of the foot. The thick layer of skin on the sole of the foot in particular is an ideal breeding ground for fungi. Longer-term treatment may therefore be necessary. This is a common problem in people with immunodeficiency.
If the treatment fails, this is often due to
- incorrect treatment by the patient,
- a misdiagnosis or
- lack of knowledge about the patient's immunodeficiency.
Body hygiene
Once the skin fungus has established itself in the skin, treatment can be lengthy and unpleasant.
The most important causes of a fungal infection are poor hygienic conditions. Fungal skin infections can therefore be effectively prevented.
This includes careful drying after washing or bathing. Pay particular attention to body cavities such as the armpits, back of the knees and between the toes. Moisture quickly collects in these areas, making them the perfect breeding ground for fungi.
Always use your own towel that you do not share with anyone.
Clothing
Clothing worn directly on the body should be washed regularly at a temperature of at least 60 degrees. Higher temperatures efficiently destroy skin fungi.
Underwear and socks in particular must be changed every day.
Problem zone feet
Places such as bathing establishments or public showers are a breeding ground for skin fungi. Always wear bathing shoes and do not walk barefoot. This also applies to restaurants and hotels. It is better not to walk on the floor without shoes.
The choice of footwear is another important criterion. Use try-on socks when trying on shoes. This will protect you against any fungal pathogens left behind by a previous wearer.
Do you tend to have damp feet? Then switch from sturdy winter boots to lighter shoes as soon as possible in spring. The longer your feet are in a damp and stuffy environment, the faster a fungus will develop. A good routine is to clean and dry your feet well before going to bed.
As the risk of infection with skin fungus is very high, care should be taken when coming into contact with infected people. However, disinfecting your own clothing (with a spray) after contact should be sufficient.