Skin infections

What are infections?

Skin infections are diseases and conditions caused by or related to an external organism, and can include infestation by mites and insects.

Organisms can also lead to inflammatory skin diseases by provoking an innate or acquired immune reaction to them, eg acne, perioral dermatitis, seborrhoeic dermatitis.

Skin infection is more likely to occur in some circumstances.

• Exposure to a particularly virulent organism
• A break in the integrity of the skin
• A contaminated wound, eg a human or animal bite, soil
• Underlying superficial skin disease, especially eczema/dermatitis and blistering conditions
• Extremes of age
• Becoming immunocompromised due to underlying disease or condition eg diabetes, blood disorder, primary immunodeficiency, human immunodeficiency infection
• Treatment with immunosuppressive medication, particularly systemic corticosteroids, azathioprine, ciclosporin, mycophenolate, cyclophosphamide, or biologics.

What organisms cause infection?

Infectious organisms are classified as:

• Obligate pathogens
• Opportunistic pathogens
• Parasites
• Saprophytes (an organism that lives on decaying matter).

Opportunistic infections

Opportunistic infection is an infection in an immunosuppressed patient that is more frequent or severe because of immune suppression. They can be caused by common infectious organisms (such as Staphylococcus aureus, Candida albicans or Herpes simplex) or ones that rarely infect healthy individuals (such as nocardia, bartonella, atypical mycobacteria, cytomegalovirus, cryptocococcus and other systemic mycoses (deep fungal infections).

Disease can be due to the following classes of organism:

• Arthropod infestation, bites and stings from insects and mites
• Protozoal infection
• Bacterial infection
• Yeast and fungal infection
• Viral infection.

Harmless microbes

Human skin is not sterile but is colonised by many microorganisms — the microbiota.

Prevention of infection

Optimal health is required to prevent and treat an infection.

Minimise the risk of lacerations, abrasions, thermal and chemical burns, animal bites and insect bites.

• Avoid injury where possible
• Protect from injury and bites using clothing and instruments
• Maintain a clean environment; wash utensils and work surfaces
• Wash hands thoroughly after food preparation and gardening
• Mitigate injury, eg clean wounds thoroughly, apply dressings and bandage to reduce swelling
• Use of insect repellents
• Actively treat acute and chronic inflammatory skin disease.

Bear in mind that excessive hygienic measures may be counterproductive if they lead to:

• Removal of a protective microbiota
• A shift to more pathogenic organisms within the microbiota
• A shift to strains of organisms that are more resistant to treatment
• Removal of the outer layer of skin, damaging skin barrier function.

When should infection be treated?

It is not always necessary to actively treat minor skin infections (eg, impetigo, folliculitis, tinea pedis, tinea unguium and herpes simplex), as these will settle on their own, at least in healthy individuals. Tackling infection often enhances natural immunity to them.

However, some infections should always be treated to prevent:

• Chronic disease in the individual, eg Lyme disease
• Contagion to other individuals, eg tuberculosis and sexually transmitted infections.

What is the treatment for the infection?

Treatment of infection depends on the cause, its severity and its sensitivity to the proposed agent.

• Protozoa are treated with antiprotozoal agents including metronidazole, ornidazole, tinidazole, eflornithine, paromycin, pentamidine, pyrimethamine, furazolidone and melarsoprol.
• Bacterial infection is treated with topical, oral and injected antibiotics.
• Fungal infection is treated with topical and oral antifungal agents.
• A viral infection is treated with antiviral agents such as aciclovir.