Fungal and Arthropod Skin Diseases

Several types of fungi grow on human skin, typically confined to the stratum corneum, or outermost layer of skin. Examples include tinea capitis, or fungal infection of the scalp. Also known as ringworm, tinea capitis is caused by fungi from the Trichophyton or Microsporum genus and most commonly occurs in children. It is highly contagious, spreading through direct or indirect (use of same comb or hat) contact. Typically the infection results in hair loss in patches and mild redness of the scalp, plus crust and scale formation. Tinea barbae is a fungal infection (T. rubrum) affecting the beard area in adult men. Tinea corporis (M. canis) is a superficial fungal infection of the skin that can occur anywhere on the body and can affect people of all ages.

Predisposing factors that lead to fungal skin infections, also called dermatophytoses, include excessive heat and humidity or areas of the body where the skin folds on itself. Tinea cruris (T. rubrum or Candida albicans) is a dermatophytosis of the inguinal region of the body, also called jock itch, and tinea pedis (T. rubrum or T. mentagrophytes), or athlete's foot, is a fungal infection of the feet. Athlete's foot affects 20% to 25% of the global population and manifests itself by diffuse scaling and redness in the area between the toes. If the infection spreads to the toenails, the condition is called onychomycosis. Fungal skin infections are typically treated with topical over-the-counter antifungal ointments that contain clotrimazole, miconazole, or terbinafine.

Harmful skin arthropods include the head louse, crab louse, and body louse (collectively called Pediculus humanus), which cause the skin condition pediculosis. Pediculus humanus is contracted through direct (touching), indirect (hairbrush, clothing), or sexual contact. Pediculosis is a pruritic, or itchy, skin disease that involves the lice or their eggs attaching themselves to the hair shafts. The lice survive by biting and ingesting small amounts of blood from their human host. Another harmful mite is Sarcoptes scabiei, the causative organism of scabies. In it, the female mite burrows underneath the keratin, or outermost, layer of the skin. These burrows can actually be seen as linear streaks on the skin between the finger digits, palms, wrists, periareolar skin in women, and genital skin in men. Scabies is highly pruritic and is spread via direct contact with others or through indirect contact through items such as clothing and blankets used by the infected person. Both P. humanus and S. scabiei are treated with topical ointments or washes with insecticidal properties. Treatments with permethrin as the active ingredient are the most widely used.