A recent retrospective study of all cases of Ecthyma gangrenosum from 2004-2010 in a university hospital in Mexico shows that neutropenia in immunocompromised patients is the most common risk factor for ecthyma gangrenosum.

A skin and skin structure infection (SSSI), also referred to as skin and soft tissue infection (SSTI) or acute bacterial skin and skin structure infection (ABSSSI), is an infection of skin and associated soft tissues (such as loose connective tissue and mucous membranes). The pathogen involved is usually a bacterial species. Such infections often requires treatment by antibiotics.

Until 2008, two types were recognized, complicated skin and skin structure infection (cSSSI) and uncomplicated skin and skin structure infection (uSSSI). "Uncomplicated" SSSIs included simple abscesses, impetiginous lesions, furuncles, and cellulitis. "Complicated" SSSIs included infections either involving deeper soft tissue or requiring significant surgical intervention, such as infected ulcers, burns, and major abscesses or a significant underlying disease state that complicates the response to treatment. Superficial infections or abscesses in an anatomical site, such as the rectal area, where the risk of anaerobic or gram-negative pathogen involvement is higher, should be considered complicated infections. The two categories had different regulatory approval requirements. The uncomplicated category (uSSSI) is normally only caused by "Staphylococcus aureus" and "Streptococcus pyogenes", whereas the complicated category (cSSSI) might also be caused by a number of other pathogens. In cSSSI, the pathogen is known in only about 40% of cases.

Because cSSSIs are usually serious infections, physicians do not have the time for a culture to identify the pathogen, so most cases are treated empirically, by choosing an antibiotic agent based on symptoms and seeing if it works. For less severe infections, microbiologic evaluation via tissue culture has been demonstrated to have high utility in guiding management decisions. To achieve efficacy, physicians use broad-spectrum antibiotics. This practice contributes in part to the growing incidence of antibiotic resistance, a trend exacerbated by the widespread use of antibiotics in medicine in general. The increased prevalence of antibiotic resistance is most evident in methicillin-resistant "Staphylococcus aureus" (MRSA). This species is commonly involved in cSSSIs, worsening their prognosis, and limiting the treatments available to physicians. Drug development in infectious disease seeks to produce new agents that can treat MRSA.

Since 2008, the U.S. Food and Drug Administration has changed the terminology to "acute bacterial skin and skin structure infections" (ABSSSI). The Infectious Diseases Society of America (IDSA) has retained the term "skin and soft tissue infection".

Systemic mycoses due to opportunistic pathogens are infections of patients with immune deficiencies who would otherwise not be infected. Examples of immunocompromised conditions include AIDS, alteration of normal flora by antibiotics, immunosuppressive therapy, and metastatic cancer. Examples of opportunistic mycoses include Candidiasis, Cryptococcosis and Aspergillosis.

The elderly and those with a weakened immune system are especially vulnerable to contracting cellulitis. Diabetics are more susceptible to cellulitis than the general population because of impairment of the immune system; they are especially prone to cellulitis in the feet, because the disease causes impairment of blood circulation in the legs, leading to diabetic foot or foot ulcers. Poor control of blood glucose levels allows bacteria to grow more rapidly in the affected tissue, and facilitates rapid progression if the infection enters the bloodstream. Neural degeneration in diabetes means these ulcers may not be painful, thus often become infected. Those who have suffered poliomyelitis are also prone because of circulatory problems, especially in the legs.

Immunosuppressive drugs, and other illnesses or infections that weaken the immune system, are also factors that make infection more likely. Chickenpox and shingles often result in blisters that break open, providing a gap in the skin through which bacteria can enter. Lymphedema, which causes swelling on the arms and/or legs, can also put an individual at risk.

Diseases that affect blood circulation in the legs and feet, such as chronic venous insufficiency and varicose veins, are also risk factors for cellulitis.

Cellulitis is also common among dense populations sharing hygiene facilities and common living quarters, such as military installations, college dormitories, nursing homes, oil platforms, and homeless shelters.

Fungal infections of the skin were the 4th most common skin disease in 2010 affecting 984 million people.

Horses may acquire cellulitis, usually secondarily to a wound (which can be extremely small and superficial) or to a deep-tissue infection, such as an abscess or infected bone, tendon sheath, or joint. Cellulitis from a superficial wound usually creates less lameness (grade 1–2 of 5) than that caused by septic arthritis (grade 4–5). The horse exhibits inflammatory edema, which is hot, painful swelling. This swelling differs from stocking up in that the horse does not display symmetrical swelling in two or four legs, but in only one leg. This swelling begins near the source of infection, but eventually continues down the leg. In some cases, the swelling also travels distally. Treatment includes cleaning the wound and caring for it properly, the administration of NSAIDs, such as phenylbutazone, cold hosing, applying a sweat wrap or a poultice, and mild exercise. Veterinarians may also prescribe antibiotics.

Cellulitis is also seen in staphylococcal and corynebacterial mixed infections in bulls.

Parasitic infestations, stings, and bites in humans are caused by several groups of organisms belonging to the following phyla: Annelida, Arthropoda, Bryozoa, Chordata, Cnidaria, Cyanobacteria, Echinodermata, Nemathelminthes, Platyhelminthes, and Protozoa.

Virus-related cutaneous conditions are caused by two main groups of viruses–DNA and RNA types–both of which are obligatory intracellular parasites.

The main organism associated with ecthyma gangrenosum is "Pseudomonas aeruginosa". However, multi-bacterial cases are reported as well. Prevention measures include practicing proper hygiene, educating the immunocompromised patients for awareness to avoid possible conditions and seek timely medical treatment.

Tinea corporis is caused by a tiny fungus known as dermatophyte. These tiny organisms normally live on the superficial skin surface, and when the opportunity is right, they can induce a rash or infection.

The disease can also be acquired by person-to-person transfer usually via direct skin contact with an infected individual. Animal-to-human transmission is also common. Ringworm commonly occurs on pets (dogs, cats) and the fungus can be acquired while petting or grooming an animal. Ringworm can also be acquired from other animals such as horses, pigs, ferrets and cows. The fungus can also be spread by touching inanimate objects like personal care products, bed linen, combs, athletic gear, or hair brushes contaminated by an affected person.

Individuals at high risk of acquiring ringworm include those who:

- Live in crowded, humid conditions.

- Sweat excessively, as sweat can produce a humid wet environment where the pathogenic fungi can thrive. This is most common in the armpits, groin creases and skin folds of the abdomen.

- Participate in close contact sports like soccer, rugby, or wrestling.

- Wear tight, constrictive clothing with poor aeration.

- Have a weakened immune system (e.g., those infected with HIV or taking immunosuppressive drugs).

Globally, fungal infections affect about 15% of the population and affects one out of five adults. Athlete's foot is common in individuals who wear occlusive shoes. Countries and regions where going barefoot is more common experience much lower rates of athlete's foot than do populations which habitually wear shoes; as a result, the disease has been called "a penalty of civilization". Studies have demonstrated that men are infected 2–4 times more often than women.

According to the NCAA Wrestling Rules and Interpretations, used by all high schools in the United States: "Infection control measures, or measures that seek to prevent the spread of disease, should be utilized to reduce the risks of disease transmission. Efforts should be made to improve wrestler hygiene practices, to utilize recommended procedures for cleaning and disinfection of surfaces, and to handle blood and other bodily fluids appropriately. Suggested measures include: promotion of hand hygiene practices; educating athletes not to pick, squeeze, or scratch skin lesions; encouraging athletes to shower after activity; educating athletes not to share protective gear, towels, razors or water bottles; ensuring recommended procedures for cleaning and disinfection of wrestling mats, all athletic equipment, locker rooms, and whirlpool tubs are closely followed; and verifying clean up of blood and other potentially infectious materials." More ways of prevention include wearing long sleeve shirts and sweatpants to limit

the amount of skin to skin contact. A wrestler should also not share their

equipment with other teammates and should regularly check their skin for any lesions or other signs of outbreaks. Body wipes are also common to see Coaches must also enforce the disinfecting and sanitary cleansing of the wrestling mats and other practice areas. This can greatly limit the spread of skin infections that can infect an individual indirectly.

One high school wrestling coach from Southern California described his methods of prevention using three simple procedures. “Keep the mats [clean]…you’ve got to bleach and mop them every day before practice. Along the same lines, gear should also be washed regularly, especially headgear…Most importantly, the wrestlers need to shower immediately after practices. If one kid doesn’t, and he gets [infected], it can spread to everyone else on the team within a week. I’ve had it happen before, to the point where some schools won’t allow any of our guys to wrestle in a meet. When this happens, it’s a huge blow to the school’s record and reputation. In the future, we are less likely to be invited to exclusive tournaments in the coming year.”

At the start of each wrestling meet, trained referees examine the skin of all wrestlers before any participation. During this examination, male wrestlers are to wear shorts; female wrestlers are only permitted to wear shorts and a sports bra. Open wounds and infectious skin conditions that cannot be adequately protected are considered grounds for disqualification from both practice and competition. This essentially means that the skin condition has been deemed as non-infectious and adequately medicated, covered with a tight wrapping and proper ointment. In addition, the wrestler must have developed no new lesions in the 72 hours before the examination. Wrestlers who are undergoing treatment for a communicable skin disease at the time of the meet or tournament shall provide written documentation to that effect from a physician. This documentation should include the wrestler’s diagnosis, culture results (if possible), date and time therapy began, and the exact names of medication for treatment. These measures aren’t always successful, and the infection is sometimes spread regardless.

Tinea corporis is moderately contagious and can affect both humans and pets. If a person acquires it, the proper measures must be taken to prevent it from spreading. Young children in particular should be educated about the infection and preventive measures: avoid skin to skin contact with infected persons and animals, wear clothing that allows the skin to breathe, and don't share towels, clothing or combs with others. If pets are kept in the household or premises, they should get the animal checked for tinea, especially if hair loss in patches is noticed or the pet is scratching excessively. The majority of people who have acquired tinea know how uncomfortable the infection can be. However, the fungus can easily be treated and prevented in individuals with a healthy immune system.

Erythrasma is caused by "Corynebacterium minutissimum". This bacteria tends to thrive in mostly moist and warm environments. Great contributors are poor hygiene, obesity, hyperhidrosis, aging, diabetes mellitus, and a poor immune system. Only some of the causable factors can be looked at for prevention. Hygiene can be improved, along with avoiding moist and warm environments. The other medical factors causing the erythrasma are underlying diseases that cannot be prevented as easily, which at times, can make this condition inevitable.

"Corynebacterium minutissimum" is the bacteria that causes this infection, often club shaped rods when observed under a microscope following a staining procedure, which is a result of snapping division which makes them look like a picket fence. This bacteria is gram positive which means it has a very thick cell wall that cannot be easily penetrated.Electron microscopy confirms the bacterial nature of erythrasma, it shows decreased electron density in keratinized cells at the sites of proliferation. This means that the bacteria causes erythrasma by breaking down keratin Fibrils in the skin. "Corynebacterium minutissimum" consumes carbohydrates such as glucose, dextrose, sucrose, maltose, and mannitol.

Erythrasma manifests mostly in slightly webbed spaces between toes (or other body region skin folds like the thighs/groin area) in warm atmospheric regions, more prevalent in dark skinned humans. As a person ages, they are more susceptible to this infection. This bacterium is not only found in warm atmospheric regions, but also warm and sweaty parts of the human body. "Corynebacterium minutissimum" survives the best here due to the encouraged fungal growth in these regions and allows it to replicate. It is more prevalent in African Americans due to their skin pigmentation.

Most cases of molluscum contagiosum will clear up naturally within two years (usually within nine months). So long as the skin growths are present, there is a possibility of transmitting the infection to another person. When the growths are gone, the possibility of spreading the infection is ended.

Unlike herpesviruses, which can remain inactive in the body for months or years before reappearing, molluscum contagiosum does not remain in the body when the growths are gone from the skin and will not reappear on their own.

Approximately 122 million people were affected worldwide by molluscum contagiosum as of 2010 (1.8% of the population).

Guttate psoriasis accounts for approximately 2% of psoriasis cases.

Genetic and environmental factors can influence the predilection for guttate psoriasis. Human leukocyte antigens, especially those in the HLA-C group are associated with the skin disorder. Beta-hemolytic streptococci infection is the major contributing environmental factor. The typical route of infection is the upper respiratory system. Rarely it is also caused by a skin infection surrounding the anus (perianal streptococcal dermatitis).

Besides being exposed to any of the modes of transmission presented above, there are additional risk factors that increase one's chance of contracting athlete's foot. Persons who have had athlete's foot before are more likely to become infected than those who have not. Adults are more likely to catch athlete's foot than children. Men have a higher chance of getting athlete's foot than women. People with diabetes or weakened immune systems are more susceptible to the disease. HIV/AIDS hampers the immune system and increases the risk of acquiring athlete's foot. Hyperhidrosis (abnormally increased sweating) increases the risk of infection and makes treatment more difficult.

Bacterial intertrigo can be caused by "Streptococci" and "Corynebacterium minutissimum".

With no particular affinity to any particular ethnic group, seen in all age groups and equally amongst males and females, the precise prevalence is not known.

An intertrigo usually develops from the chafing of warm, moist skin in the areas of the inner thighs and genitalia, the armpits, under the breasts, the underside of the belly, behind the ears, and the web spaces between the toes and fingers. An intertrigo usually appears red and raw-looking, and may also itch, ooze, and be sore. Intertrigos occur more often among overweight individuals, those with diabetes, those restricted to bed rest or diaper use, and those who use medical devices, like artificial limbs, that trap moisture against the skin. Also, there are several skin diseases that can cause an intertrigo to develop, such as dermatitis or inverse psoriasis.

HPV is spread by direct and indirect contact from an infected host. Avoiding direct contact with infected surfaces such as communal changing rooms and shower floors and benches, avoiding sharing of shoes and socks and avoiding contact with warts on other parts of the body and on the bodies of others may help reduce the spread of infection. Infection is less common among adults than children.

As all warts are contagious, precautions should be taken to avoid spreading them. Recommendations include:

- cover them with an adhesive bandage while swimming

- wear flip-flops when using communal showers

- should not share towels.

Plantar warts are not prevented by inoculation with HPV vaccines because the warts are caused by different strains of HPV. Gardasil protects against strains 6, 11, 16, and 18, and Cervarix protects against 16 and 18, whereas plantar warts are caused by strains 1, 2, 4, and 63.