Diagnosis is made by clinical observation and the following tests.

(1) Gram stain of the fluid from pustules or bullae, and tissue swab.

(2) Blood culture

(3) Urine culture

(4) Skin biopsy

(5) Tissue culture

Magnetic resonance imaging can be done in case of ecthyma gangrenosum of plantar foot to differentiate from necrotizing fasciitis.

Dempster-Shafer Theory is used for detecting skin infection and displaying the result of the detection process.

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".

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.

Other conditions that may mimic cellulitis include deep vein thrombosis, which can be diagnosed with a compression leg ultrasound, and stasis dermatitis, which is inflammation of the skin from poor blood flow. Signs of a more severe infection such as necrotizing fasciitis or gas gangrene that would require prompt surgical intervention include purple bullae, skin sloughing, subcutaneous edema, and systemic toxicity. Misdiagnosis can occur in up to 30% of people with suspected lower-extremity cellulitis, leading to 50,000 to 130,000 unnecessary hospitalization and $195 to $515 million in avoidable healthcare spending annually in the United States.

Associated musculoskeletal findings are sometimes reported. When it occurs with acne conglobata, hidradenitis suppurativa, and pilonidal cysts, the syndrome is referred to as the follicular occlusion triad or tetrad.

Lyme disease can be misdiagnosed as staphylococcal- or streptococcal-induced cellulitis. Because the characteristic bullseye rash does not always appear in people infected with Lyme disease, the similar set of symptoms may be misdiagnosed as cellulitis. Standard treatments for cellulitis are not sufficient for curing Lyme disease. The only way to rule out Lyme disease is with a blood test, which is recommended during warm months in areas where the disease is endemic.

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.

Diagnosis is made on the appearance; the virus cannot routinely be cultured. The diagnosis can be confirmed by excisional biopsy.

Histologically, molluscum contagiosum is characterized by molluscum bodies in the epidermis, above the stratum basale, which consist of large cells with abundant granular eosinophilic cytoplasm (accumulated virions) and a small peripheral nucleus.

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.

In those who have previously had cellulitis, the use of antibiotics may help prevent future episodes. This is recommended by CREST for those who have had more than two episodes.

Keeping the skin clean and dry, as well as maintaining good hygiene, will help larger topical mycoses. Because fungal infections are contagious, it is important to wash after touching other people or animals. Sports clothing should also be washed after use.

Superficial scrapes of skin examined underneath a microscope may reveal the presence of a fungus. This is done by utilizing a diagnostic method called KOH Test, wherein the skin scrapings are placed on a slide and immersed on a dropful of potassium hydroxide solution to dissolve the keratin on the skin scrappings thus leaving fungal elements such as hyphae, septate or yeast cells viewable. If the skin scrapings are negative and a fungus is still suspected, the scrapings are sent for culture. Because the fungus grows slowly, the culture results do take several days to become positive.

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.”

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.

There are differential diagnosis' for erythrasma which includes psoriasis, candidasis, dermaphytosis, and interigo. The diagnosis can be made on the clinical picture alone. However, a simple side-room investigation with a Wood's lamp is additionally useful in diagnosing erythrasma. The ultraviolet light of a Wood's lamp causes the organism to fluoresce a characteristic coral red color, differentiating it from other skin conditions such as tinea versicolor, which may fluoresce a copper-orange color. Another route to differentiate erythrasma would be through bacterial and mycology related cultures to compare/contrast normal results to these findings. These are both non-invasive routes.

Erythrasma is often mistakenly diagnosed as dermatophytic infection which is a fungal infection and not a bacterial infection. The difference here is that fungi are multicellular and eukaryotes while bacteria are single celled prokaryotes. This is vital to differentiate because of the way they reproduce will indicate how the infection will spread throughout the human body.

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.

Guttate psoriasis can typically be diagnosed by clinical examination alone. If necessary, a skin biopsy can be used to support the diagnosis.

Intertrigo can be diagnosed clinically by a medical professional after taking a thorough history and performing a detailed physical examination. Many other skin conditions can mimic intertrigo's appearance including erythrasmascabies, pyoderma, atopic dermatitis, candidiasis, and seborrheic dermatitis, and fungal infections of the superficial skin caused by "Tinea versicolor" or "Tinea corporis".

Recent research for Erythrasma is mainly focused on the treatments and which methods work best to treat the patient depending on the severity of the condition. In a 2016 study performed by Prathyusha Prabhakar and H. Hema, they looked into comparing 2% clotrimazole cream and 2% Fusidic cream in treating erythrasma. This was a one year long hospital based study in South India that resulted in stating that the groin was the most common site for the symptoms of itching and discloloration being predominant and also mostly in men. The general conclusion made was that topical 2% fusidic acid cream was found to be more effective than 2% clotrimazole cream in patients with erythrasma. The topical 2% clotrimazole cream was more effective only when an associated fungal infection was present.

Another study performed in early 2017 by Tanya Grewal and Philip Cohen looked directly at mupirocin 2% ointment monotherapy. This study was done with nine males who showed a presence of erythrasma at bilateral inguinal folds, medial thighs, and axillae. After initial diagnosis by Wood lamp's examination to confirm the diagnosis, the antibiotic cream was distributed. Mupirocin is a topical antibiotic that is usually used to treat Streptococcus and Staphylococcus infections. After 2-4 weeks of use, the erythrasma seemed to clear up. They were able to conclude that the application of 2% Mupirocin ointment monotherapy twice a day, everyday is a great consideration for a first line of treatment for erythrasma.

A study done in 2011 by M. Inci and G. Serarslan revolved around detecting the frequency and risk factors of interdigital erythrasma in patients who were possibly diagnosed with Tinea pedis. The study was done with 122 people who had a confirmed diagnoses of erythrasma through the Wood's lamp method. The results showed that erythrasma was more prevalent in males who were over the age of 40 years. Their conclusions were that erythrasma is a common condition and can also easily mimic other infections such as tinea pedis and that gram staining is a better tool to differentiate the bacteria and it's mechanism than the Wood's lamp method.

When visiting a doctor, the basic diagnosis procedure applies. This includes checking the patient's medical history and medical record for risk factors, a medical interview during which the doctor asks questions (such as about itching and scratching), and a physical examination. Athlete's foot can usually be diagnosed by visual inspection of the skin and by identifying less obvious symptoms such as itching of the affected area.

If the diagnosis is uncertain, direct microscopy of a potassium hydroxide preparation of a skin scraping (known as a KOH test) can confirm the diagnosis of athlete's foot and help rule out other possible causes, such as candidiasis, pitted keratolysis, erythrasma, contact dermatitis, eczema, or psoriasis. Dermatophytes known to cause athlete's foot will demonstrate multiple septate branching hyphae on microscopy.

A Wood's lamp (black light), although useful in diagnosing fungal infections of the scalp (tinea capitis), is not usually helpful in diagnosing athlete's foot, since the common dermatophytes that cause this disease do not fluoresce under ultraviolet light.

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

Diagnosis of Tinea Barbae will firstly include questions being asked from doctors about interactions with farm animals and lifestyle experiences. Doctor will then gain knowledge on possible disease by microscopy, this is viewing the skin under a microscope to get an enlarge view of infected area. Skin scraping and removal of hairs on infected area will occur for medical examination. To acquire causation of Tinea Barbae putting infected area under ultraviolet light can achieve this, as infection caused by animal and human contact will not show up as fluorescent under the ultraviolet light, compared to other causes of this disease.

Intertrigo is treated by addressing associated infections, by removing moisture from the site, and by using substances at the site to help maintain skin integrity. If the individual is overweight, losing weight may also help. Relapses of intertrigo are common.

Keeping the area of the intertrigo dry and exposed to the air can help prevent recurrences, as can removing moisture from the area using absorbent fabrics or body powders, including plain cornstarch and judiciously used antiperspirants.

Greases, oils, and barrier ointments, may help by protecting skin from moisture and from friction. Antifungal powders, most commonly clotrimazole 1%, may also be used in conjunction with a barrier ointment. Diaper rash ointment can also help.

Fungal infections associated with intertrigo may be treated with prescription antifungals applied directly to the skin (in most cases) or systemic antifungals, including fluconazole, nystatin, and griseofulvin.

Intertrigo is also a known symptom of vitamin B6 deficiency.

In approximately half of suspected nail fungus cases there is actually no fungal infection, but only some nail dystrophy. Before beginning oral antifungal therapy the health care provider should confirm a fungal infection. Administration of treatment to persons without an infection is unnecessary health care and causes needless exposure to side effects.

Guttate psoriasis accounts for approximately 2% of psoriasis cases.

For severe or refractory cases of athlete's foot oral terbinafine is more effective than griseofulvin. Fluconazole or itraconazole may also be taken orally for severe athlete's foot infections. The most commonly reported adverse effect from these medications is gastrointestinal upset.