Introduction

The skin, being the largest organ of the body, acts as a physical and immunological barrier against the external environment. However, it is constantly exposed to various microorganisms — bacteria, viruses, fungi, and parasites — that can lead to a wide spectrum of infections. Infectious skin diseases are among the most frequent reasons for dermatological consultations worldwide, particularly in tropical and developing countries where heat, humidity, overcrowding, and poor hygiene facilitate their spread.

These infections can range from mild and self-limiting to severe, life-threatening conditions requiring urgent intervention. Understanding their clinical features, causative organisms, and management is crucial for early diagnosis and appropriate treatment.

1. Bacterial Skin Infections

a. Impetigo

Causative agent: Staphylococcus aureus or Streptococcus pyogenes.
Clinical features: Highly contagious, characterized by honey-colored crusted lesions commonly seen around the nose, mouth, and extremities in children.
Treatment: Topical mupirocin or fusidic acid; oral antibiotics (dicloxacillin, cephalexin) for extensive lesions.

b. Cellulitis and Erysipelas

Causative agent: Streptococcus pyogenes and Staphylococcus aureus.
Clinical features: Painful erythematous swelling with warmth and tenderness; erysipelas has well-demarcated edges.
Treatment: Systemic antibiotics (amoxicillin-clavulanate, cefazolin, or clindamycin).

c. Folliculitis, Furuncles, and Carbuncles

Causative agent: S. aureus.
Clinical features: Folliculitis involves small pustules around hair follicles; furuncles (boils) are deeper, and carbuncles are coalesced abscesses.
Treatment: Warm compresses, incision and drainage for abscesses, oral antistaphylococcal antibiotics.

d. Necrotizing Fasciitis

Causative agent: Polymicrobial, often including Streptococcus pyogenes and anaerobes.
Clinical features: Rapidly spreading necrosis of fascia, severe pain, systemic toxicity.
Treatment: Surgical emergency requiring debridement and broad-spectrum IV antibiotics.

2. Fungal Skin Infections (Dermatophytoses and Yeast Infections)

a. Dermatophytosis (Tinea or Ringworm)

Causative agents: Trichophyton, Microsporum, Epidermophyton species.
Clinical variants:
- Tinea corporis – ring-shaped plaques on body.
- Tinea cruris – groin infection (“jock itch”).
- Tinea capitis – scalp involvement, often in children.
- Tinea pedis – athlete’s foot.
Treatment: Topical antifungals (clotrimazole, terbinafine); oral antifungals (itraconazole, griseofulvin) for extensive or scalp infections.

b. Candidiasis

Causative agent: Candida albicans (yeast).
Clinical features: Moist, red patches with satellite pustules, often in intertriginous areas (axilla, groin, under breasts).
Treatment: Topical azoles (clotrimazole, miconazole), systemic fluconazole for recurrent cases.

c. Pityriasis Versicolor

Causative agent: Malassezia furfur (lipophilic yeast).
Clinical features: Hypo- or hyperpigmented scaly macules on trunk and upper arms; more visible in humid climates.
Treatment: Topical selenium sulfide, ketoconazole shampoo, or oral itraconazole.

3. Viral Skin Infections

a. Herpes Simplex Virus (HSV)

Types: HSV-1 (oral) and HSV-2 (genital).
Clinical features: Painful grouped vesicles on erythematous base; recurrent attacks triggered by stress, fever, or sunlight.
Treatment: Oral acyclovir or valacyclovir; topical therapy for mild lesions.

b. Varicella-Zoster Virus (VZV)

Chickenpox: Vesicular rash in crops (“dew drops on rose petals”).
Herpes Zoster (Shingles): Reactivation of VZV causing dermatomal vesicular eruption with severe pain.
Treatment: Antivirals (acyclovir, valacyclovir) within 72 hours; analgesics for neuralgia.

c. Warts (Human Papillomavirus – HPV)

Clinical types:
- Common warts (hands)
- Plantar warts (feet)
- Flat warts (face)
- Genital warts (condyloma acuminata)
Treatment: Cryotherapy, salicylic acid, electrocautery, or topical imiquimod.

d. Molluscum Contagiosum

Causative agent: Poxvirus.
Clinical features: Umbilicated, flesh-colored papules, common in children and immunocompromised adults.
Treatment: Curettage, cryotherapy, or topical agents (tretinoin, potassium hydroxide).

4. Parasitic Skin Infections

a. Scabies

Causative agent: Sarcoptes scabiei mite.
Clinical features: Intense nocturnal itching with burrows and papules in web spaces, wrists, genitalia.
Treatment: Permethrin 5% cream, ivermectin (oral); treat all household contacts.

b. Pediculosis (Lice Infestation)

Types:
- Pediculus humanus capitis (head lice)
- Pediculus humanus corporis (body lice)
- Phthirus pubis (pubic lice)
Treatment: Permethrin lotion/shampoo, fine-tooth combing, laundering of clothes and bedding.

c. Cutaneous Leishmaniasis

Causative agent: Leishmania species (transmitted by sandfly).
Clinical features: Painless ulcer with raised borders (“oriental sore”).
Treatment: Intralesional antimonials, amphotericin B, or miltefosine.

Prevention and Public Health Perspective

Personal hygiene: Regular bathing, clean clothing, and avoiding sharing of towels or razors.
Environmental control: Reducing overcrowding, improving sanitation, and maintaining dry skin folds.
Vaccination: Varicella and HPV vaccines reduce viral skin infections significantly.
Early diagnosis: Prompt identification and treatment prevent complications and transmission.

Conclusion

Infectious skin diseases are common yet preventable and treatable. Awareness among healthcare professionals and the public, combined with good hygiene practices and timely therapy, can significantly reduce their burden. Recognizing the clinical patterns of bacterial, fungal, viral, and parasitic infections remains a vital skill for clinicians, particularly in primary care and dermatology settings.