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Skin infections

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The skin is the body's main defence barrier against the invasion and growth of external infectious agents which we are exposed to 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 almost everyone suffers from them at some point in their life.

Causes of skin infections

There are several causes of skin infections.

Having skin with an altered barrier function (this occurs in irritative dermatitis, acute eczema, ulcers, small wounds, erosions, the presence of foreign objects such as piercings, etc.) facilitates the entry and colonisation of infectious agents.

There are other predisposing factors that can favour the appearance of skin infections, such as the presence of exudate (liquid that leaks from the blood vessels to nearby tissue), an increase in temperature, immunosuppression (caused by stress, bad eating habits, corticosteroid therapy, etc.); suffering from various diseases (atopic dermatitis, diabetes, obesity, poor peripheral circulation, etc.), or the use of antibiotics that unbalance the resident flora of the body.

Viral infections

Among viral infections, the following stand out:

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.

Herpes Simplex is the most common viral infection of the herpes viruses. Up to 80% of the population are asymptomatic carriers of the virus. The herpes virus known as the varicella-zoster virus is less prevalent. Both herpes viruses cause an initial infection, which is usually asymptomatic in the case of herpes simplex and varicella in the case of herpes zoster. These viruses then become latent and can be reactivated after a triggering factor, such as exposure to the sun, 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).

Infections by the Human Papilloma Virus, such as common warts and verrucas, are very common. Common warts are defined proliferations of the same skin colour with a rough surface. They usually appear in exposed areas, such as the hands and knees, but they can be located in any other area of the skin. Plantar warts (verrucas) are specific warts on the soles of the feet, with an appearance similar to calluses. They are painful and differ from calluses because of the presence of multiple black spots on their surface due to the blood capillaries. Sometimes they are grouped in thickened plaques, called mosaic warts.

Bacterial infections

Bacterial skin infections are skin infections caused by pyogenic bacteria (pus producing), mainly staphylococci and streptococci. They are relatively common in clinical practice, accounting for 17% of all paediatric visits, affecting patients of all ages, particularly children and patients with associated risk factors.

They can be divided into primary infections, developing over previously healthy skin; and secondary infections, that occur over previously injured or impaired skin, such as eczema, ulcers, dermatomycosis, etc. They can affect only the outermost layers, from the epidermis, like with impetigo, to skin appendages, such as folliculitis, or the entire depth of the skin.

It is a highly contagious superficial infection (it can become an epidemic in nurseries, schools, families), affecting preschool and school children in particular. Poor hygiene, humid and warm climates, minor injuries, etc., are some of the 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, with shaving being a vector of infection transmission in the same individual.

Fungal infections

There are different types of 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 visits to the dermatology clinic.

Examples are Pityriasis versicolor, Dermatophytosis or Ringworms and Candidiasis.