Skin infection

Tiny germs can get on your skin.

These germs can make your skin red. It can also make it swell. This can happen to people and animals.

Some germs cause itchy spots. Other germs make yellow crusts. These crusts can be around the mouth.

Some germs live in the hair. This can make the hair area red. Other germs like warm, wet places.

Some germs make small bumps. These can be on your hands. They can also be on your feet.

It is good to learn about germs. They can change how our skin looks.

Tiny germs can get into your skin. This is called a skin infection. It can affect humans and animals. These germs can cause skin to swell or turn red.

Bacteria are one type of germ that causes infections. Cellulitis is a type of bacterial infection. It makes the deep layers of skin swell. Some bacteria cause impetigo. This is common in young children. It makes yellow, honey-colored crusts around the mouth or nose.

Fungi are other germs that cause problems. Ringworm is a common fungal infection. It likes warm and wet places. Fungi can also affect your nails. This is called onychomycosis. It can make nails thick or brittle.

Viruses can also cause skin issues. Warts are small bumps caused by a virus. They can grow on the soles of your feet. Chickenpox is another virus. It causes an itchy rash with blisters. Hand, foot, and mouth disease is also viral. It often affects infants and children. It causes a rash on the hands and feet.

Caption: This photo shows a leg with cellulitis. It looks very swollen.

A skin infection happens when germs enter the skin of humans or animals. These germs can also affect soft tissues like the layers under the skin. Some people call these skin and soft tissue infections, or SSTIs. These are different from dermatitis, which is just skin inflammation. However, an infection can lead to inflammation called infective dermatitis.

Skin infections are very common around the world. In 2013, bacterial skin infections affected about 155 million people. During that same year, cellulitis occurred in about 600 million people.

Bacteria are one main cause of these infections. Cellulitis is a type of infection that makes the skin layers swell. It can be purulent or non-purulent depending on the symptoms. Purulent cellulitis often comes from a germ called Staphylococcus aureus. Non-purulent cellulitis is often caused by Streptococcus pyogenes.

Another bacterial infection is erysipelas, which affects the top layers of the skin. Folliculitis happens when the small holes for hair become inflamed. This can be caused by bacteria, fungi, viruses, or even tiny mites.

Impetigo is another bacterial infection that is very easy to spread. It is very common among children in preschool. This infection often creates yellow, honey-colored crusts near the mouth or nose. About 140 million people have impetigo at any given time. Most cases are nonbullous, which makes up 70% of the diagnosed cases. The other 30% are bullous cases caused by S. aureus.

In rare cases, this can lead to a serious condition called Staphylococcal Scalded Skin Syndrome.

Fungi can also cause skin, hair, or nail infections. These are sometimes called dermatomycoses. Ringworm is a common type of superficial fungal infection. It is more common in places that are warm and humid.

Some fungi, like Candida albicans, cause oral thrush on the tongue. This affects about 2 million people every year. Another type is onychomycosis, which affects the toenails. In North America, between 8.7% and 13.8% of people have it. Mycetoma is a group of infections that can start in the feet. As of 2010, these affect about one billion people globally.

Viruses and parasites are the final types of causes. Warts are small bumps caused by the human papilloma virus. Some warts, called plantar warts, grow on the soles of the feet.

Chickenpox is a very contagious disease caused by the varicella-zoster virus. In 2014, about 4.2 million serious cases required hospital stays. Another viral illness is hand, foot, and mouth disease. This is caused by enteroviruses and coxsackieviruses. It usually causes a rash on the palms and the soles of the feet.

A skin infection occurs when germs invade the skin of humans or animals. These infections can also spread to associated soft tissues. These include mucous membranes and loose connective tissue. Experts often group these under the term skin and soft tissue infections, or SSTIs. They may also be called skin and skin structure infections, or SSSIs. Acute bacterial versions are known as ABSSIs. It is important to distinguish these from dermatitis. Dermatitis is simply inflammation of the skin. However, a skin infection can cause inflammation called infective dermatitis.

Bacteria are a major cause of these conditions. One common type is cellulitis, which is a diffuse inflammation of connective tissue. It causes severe inflammation in the dermal and subcutaneous layers. Cellulitis is divided into two main types based on symptoms. Purulent cellulitis is often caused by Staphylococcus aureus. This includes both methicillin-sensitive and methicillin-resistant strains, known as MRSA. Non-purulent cellulitis is usually linked to group A beta-hemolytic streptococci. One specific pathogen is Streptococcus pyogenes. In rare cases, this can progress into necrotizing fasciitis. This is a serious and potentially fatal infection.

Other bacterial infections affect different skin depths. Erysipelas is a bacterial infection that primarily targets the superficial dermis. It often involves the superficial lymphatics as well. Unlike cellulitis, erysipelas does not reach the deeper skin layers. It is mostly caused by Streptococcus pyogenes. Another condition is folliculitis, which affects the hair follicles in the dermal layer. While bacteria like Staphylococcus aureus are common causes, other agents exist. Fungi such as Malassezia species can cause it. Viruses like the herpes simplex virus are also possible. Even tiny mites, specifically Demodex species, can cause folliculitis.

Impetigo is a highly contagious form of acute bacterial skin infection. It is very common among children in preschool. This condition is primarily associated with S. aureus and S. pyogenes. It creates characteristic yellow, honey-colored crusted lesions. These lesions usually appear around the nose, mouth, and chin. It is estimated that 140 million people are affected by impetigo globally at any time. There are two main forms: bullous and nonbullous. Nonbullous impetigo is the most common, representing about 70% of cases. The bullous form accounts for the remaining 30%. Bullous impetigo is primarily caused by S. aureus. In rare instances, it can lead to Staphylococcal Scalded Skin Syndrome, or SSSS.

Fungi can also cause infections, sometimes called dermatomycoses. These can be superficial or deep in the skin, hair, or nails. Mycetoma is a broad group of fungal infections. These typically start in the subcutaneous tissues and skin of the foot. If not treated quickly, they can reach bones and joints. This can cause osteomyelitis, which is a bone infection. Severe cases might require surgical bone resections or limb amputation. As of 2010, mycetoma affected about one billion people globally. Another common fungal infection is dermatophytosis, or ringworm. This is a superficial infection caused by species like Trichophyton, Epidermophyton, or Microsporum. It is more common in areas with high temperature and humidity. It is estimated that 20% to 25% of the world's population is affected by superficial fungal infections.

Fungal infections also affect specific areas like the mouth and nails. Oral candidiasis, or oral thrush, affects the tongue and oral mucosal membranes. It is mainly caused by Candida albicans. This fungus is part of the normal oral flora. It only causes infection when microbiota or immune barriers are impaired. This allows the fungus to overgrow. About 2 million people are affected by oral candidiasis every year. Onychomycosis is a fungal infection that predominantly affects the toenails. Two common agents are Trichophyton mentagrophytes and Trichophyton rubrum. Symptoms include nail thickening, brittleness, and discoloration. In North America, prevalence is between 8.7% and 13.8%.

Parasites and viruses represent other ways the skin becomes infected. Parasitic infestations involve many different phyla, including Arthropoda and Protozoa. Viral infections are caused by obligate intracellular agents. These can be DNA or RNA viruses. Warts are benign proliferative skin lesions caused by the human papilloma virus, or HPV. Plantar warts, or verrucae plantaris, appear as thick calluses on the soles of the feet. Other types include flat, genital, mosaic, and periungual warts. Chickenpox is another highly contagious viral disease. It is caused by the varicella-zoster virus, or VZV. It causes a pruritic, blister-like rash. In 2014, an estimated 4.2 million serious cases required hospitalization. Finally, hand, foot, and mouth disease is caused by enteroviruses and coxsackieviruses. This viral illness often causes a rash on the palms, soles, and around the mouth.