Skin Infections are diseases in which microorganisms invade, colonise or otherwise produce clinically significant disease within the skin or its associated structures. The major infectious categories include bacterial, fungal and viral infections, with parasitic infestations sometimes discussed alongside them even though they are biologically distinct. The skin normally provides a highly effective physical, chemical and immunological barrier, supported by keratin, lipids, antimicrobial peptides, resident immune cells and a diverse microbiome.
Infection becomes more likely when this barrier is disrupted by wounds, dermatitis, surgery, burns, chronic ulcers, scratching or other forms of tissue damage, although some pathogens can infect intact skin. The clinical appearance depends on the organism, depth of involvement, host immune response and anatomical site.
Skin infections can involve the epidermis, dermis, subcutaneous tissue, hair follicles, nails or deeper structures. Superficial infections may produce scaling, crusting, pustules or localised inflammation, whereas deeper infections can cause warmth, swelling, tenderness, rapidly expanding redness, tissue destruction or systemic illness. Important bacterial examples include impetigo, cellulitis, erysipelas and folliculitis; fungal diseases include dermatophyte infections and candidiasis; viral infections include herpes simplex, herpes zoster and certain viral wart disorders. The distinction between colonisation and infection is important because microorganisms may be present on healthy skin without causing disease. A positive culture therefore does not always establish that the cultured organism is responsible for the clinical process.
Host factors strongly influence susceptibility and severity. Diabetes, impaired circulation, immune suppression, chronic oedema, skin barrier disorders, obesity, advanced age and recent surgery can increase the risk of certain infections or complicate recovery. Local factors such as moisture, occlusion, friction and maceration can promote microbial growth. Some infections spread readily between people through direct contact, contaminated objects or shared environments, while others arise primarily from microorganisms already living on or around the person's skin. The microbiome is therefore relevant to both protection and disease, because normal organisms can inhibit pathogens under ordinary conditions but may become opportunistic when barriers or host defences are disrupted.
Diagnosis is generally based on clinical examination, but laboratory confirmation can be valuable when the diagnosis is uncertain, treatment failure occurs or the organism has important resistance implications. Depending on the suspected infection, investigations may include bacterial culture, fungal microscopy and culture, viral molecular testing, skin scrapings, swabs or tissue biopsy. Sampling technique matters because superficial contamination can produce misleading results. The differential diagnosis is broad because inflammatory conditions such as eczema, psoriasis, contact dermatitis and autoimmune disease can resemble infection. Conversely, infection can develop secondarily within an inflammatory skin disorder, so the presence of pre-existing dermatitis does not exclude an infectious complication.
Treatment must be matched to the pathogen and anatomical depth. Bacterial infections may require topical or systemic antibacterial drugs, fungal infections require antifungal treatment, and viral infections may require antiviral medicines when appropriate. Antibiotics do not treat fungal or viral infections, while antifungal treatment cannot eradicate bacterial disease. Treatment duration and route depend on the organism, severity, site and host factors. Antimicrobial resistance is an important limitation of indiscriminate treatment, particularly when antibiotics are used unnecessarily or incorrectly. Good antimicrobial practice therefore includes establishing the most likely diagnosis, using appropriate agents at appropriate doses and durations, and obtaining microbiological testing when it is clinically warranted.
Prevention includes maintaining skin integrity, managing chronic skin diseases, protecting wounds, practising appropriate hygiene and avoiding unnecessary sharing of personal items when infections are transmissible. Hand hygiene can reduce transmission of many pathogens, but excessive cleansing or harsh antiseptic use can damage the skin barrier and potentially increase susceptibility to irritation. Wounds should be cleaned and appropriately covered when indicated, while people with recurrent infections may require investigation of underlying risk factors. Community and healthcare settings also require infection-control practices tailored to the organism, route of transmission and resistance profile. Vaccination can prevent some infections with important cutaneous manifestations, although vaccines do not prevent every type of skin infection.
Certain skin infections can become medical emergencies. Rapidly spreading redness, severe pain, systemic illness, tissue necrosis, rapidly progressive swelling, blistering or signs of sepsis may indicate a deeper or severe infection requiring urgent assessment. Necrotising soft-tissue infections are particularly serious because tissue destruction can progress rapidly and may require emergency surgery as well as antimicrobial treatment. Facial infections near the eyes can also pose special risks because infection may spread to deeper structures. Immunocompromised people may develop atypical or unusually severe infections and may not always produce dramatic inflammatory signs, so clinical context is essential when interpreting apparently minor lesions.
Skin infections differ from non-infectious inflammatory dermatoses because microorganisms are central to the disease process, but visual appearance alone does not always provide a reliable distinction. Antibiotics should not be used simply because a rash is red, and corticosteroids can worsen certain infections if given without appropriate consideration of the diagnosis. Conversely, antimicrobial treatment may be necessary when an inflammatory disorder becomes secondarily infected.
Accurate classification requires attention to lesion morphology, speed of progression, symptoms, exposure history, host risk factors and, where necessary, microbiological evidence. The overall significance of skin infections ranges from minor self-limited conditions to invasive disease with substantial morbidity, making early recognition of severe presentations and responsible antimicrobial use important components of effective care.
