


Dermatology Dermatology

Skin infections

A cutaneous infection is an infection of the skin. The skin is the body's main defence barrier against the invasion and growth of external infectious agents, to which we are exposed daily. In part, this defence is due to the so-called resident flora, the "beneficial" microorganisms that live in the outermost surfaces of our skin (stratum corneum). When the balance is upset as a result of these external aggressions, skin infections occur. Depending on the infectious agents, skin infections can be classified as bacterial (such as impetigo and folliculitis), fungal (such as ringworm and candidiasis) or viral (such as molluscum contagiosum, herpes and warts) and are suffered by almost everyone at some point in their life.

Causes and risk factors

Having skin with an impaired barrier function (which occurs in irritative dermatitis, acute eczema, ulcers, small cuts, erosion, the presence of foreign bodies such as piercings, etc.) enhances the entrance and colonisation of infectious agents. There are other predisposing factors that can enhance the occurrence of skin infections such as the presence of exudate, increased temperature, immunosuppression (stress, bad habits, therapy with corticosteroids, etc.); suffering various diseases (atopic dermatitis, diabetes, obesity, poor peripheral blood flow, etc.),  or the use of antibiotics impairing the body's resident flora.  

Viral infections

Molluscum contagiosum

Molluscum contagiosum is a common infection caused by a poxvirus. Its lesions consist of papules with a central depression. Its is highly variable in number (it can reach into the hundreds). It particularly affects young children, causing school epidemics. It is less common in adults. They are located in any part of  the body and are generally grouped together in a specific area, but can be scattered. It is a highly contagious infection (through swimming pools, shared objects – sponges, towels, etc. -, and direct skin to skin contact). It is self-limiting, but can often remain unchanged for months or years.


Infection by the herpes virus

Herpes Simplex is the most common viral infection of the herpes viruses.Up to 80% of the population carries the virus asymptomatically. The herpes virus known as the varicella-zoster virus is less prevalent. Both herpes viruses cause a first infection, which is usually asymptomatic in the case of herpes simplex and varicella in the case of herpes zoster. Then these viruses become latent and can be reactivated after a triggering factor, such as sun exposure, fever, a banal digestive condition or a change in mood, causing recurrences (the typical herpes labialis or cold sores in the case of herpes simplex, or shingles in herpes zoster).


Human Papilloma

Infections by the Human Papilloma Virus, such as vulgar warts and genital condyloma, are very common. Vulgar warts are delimited epidermal proliferations of the same colour as the skin, with a rough texture. They usually appear in exposed areas, such as the hands and knees, but can be located in any other area of the skin. Plantar warts are specific warts found on the soles of the feet and have an appearance similar to calluses, are painful, and differ from them due to the presence of multiple black spots on their surfaces for the blood capillaries. Sometimes they are grouped together in thickened plaques, called mosaic warts.

Bacterial infections

Bacterial skin infections are skin infections caused by pyogenic bacteria (producing pus), mainly staphylococci and streptococci. They are relatively common in clinical practice, accounting for 17% of all paediatric visits, affecting patients of all ages, in particular children and patients with associated risk factors. They can be divided into primary, developing over previously healthy skin; and secondary, that occur over previously injured or impaired skin, such as eczema, ulcers, dermatomycosis, etc. They can affect only the outermost layers, from the epidermis, as with impetigo, to skin appendages, such as folliculitis, or the entire skin in depth.



It is a highly contagious superficial infection (it can be an epidemic episode in nurseries, schools, families), affecting preschool and school children in particular. Poor hygiene, humid and warm climates, minor injuries, etc., are predisposing factors. It is characterised by the onset of blisters, which upon breaking secrete a fluid that will subsequently form a golden crust.



This is the infection of the hair follicle. Multiple tiny pustules are formed, often crossed by a hair, and located in the hairiest areas.

When the part of the follicle in the dermis is affected, it is called deep folliculitis or furuncle. It mainly affects adult males, shaving being a vector of infection transmission in the same individual.

Fungal infections

Of about 100,000 fungal species identified, only 100 of them can be considered potentially pathogenic for humans.

Fungal infections or skin mycosis include very common infections caused by fungi which account for a significant part of dermatology clinical visits.

Examples are: Pityriasis versicolor, Dermatophytosis or Ringworms and Candidiasis


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