Basal cell carcinoma is the most common human malignancy, arising from basal keratinocytes with strong links to UV exposure and PTCH1/HH pathway dysregulation. It grows slowly with rare metastasis but can cause significant local destruction. Subtypes include nodular, superficial, infiltrative/morpheaform,…
Pediculosis refers to infestation by blood-sucking lice: Pediculus humanus capitis (head lice), P. humanus humanus (body lice), and Pthirus pubis (pubic or crab lice). Head lice are common in schoolchildren and spread by head-to-head contact. Body lice live in clothing…
Scabies is a pruritic infestation by the mite Sarcoptes scabiei var. hominis. Transmission is primarily via prolonged skin-to-skin contact; fomites can spread crusted scabies. Classic scabies presents with nocturnal itch and burrows/papules in characteristic locations. Crusted (Norwegian) scabies occurs in…
Tinea corporis is a superficial dermatophyte infection of glabrous skin caused by Trichophyton, Microsporum, or Epidermophyton species. It presents as annular erythematous plaques with advancing scaly borders and central clearing. Diagnosis is clinical supported by KOH microscopy. Topical antifungals are…
Tinea pedis is a dermatophyte infection of the feet, most commonly caused by Trichophyton rubrum. Clinical patterns include interdigital maceration, moccasin (hyperkeratotic) scale, and vesiculobullous eruptions. Diagnosis is clinical supported by KOH microscopy and, if needed, culture or PCR. Topical…
Cutaneous HSV infections present as grouped vesicles on an erythematous base with burning pain, evolving to erosions and crusts. HSV-1 commonly affects orolabial areas; HSV-2 is more often genital, though sites overlap due to changing epidemiology. Primary infection may be…
Herpes zoster is a reactivation of latent varicella-zoster virus (VZV) in sensory ganglia, producing a unilateral, dermatomal vesicular eruption with neuropathic pain. Complications include postherpetic neuralgia (PHN), ophthalmic zoster with vision-threatening keratitis/uveitis, and neurologic sequelae. Prompt antiviral therapy within 72…
Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue presenting with warmth, erythema, edema, and tenderness; erysipelas is a more superficial variant with raised, sharply demarcated borders, typically caused by β-hemolytic streptococci. S. aureus (including MRSA) and…
Impetigo is a highly contagious superficial bacterial skin infection, most commonly affecting children. Nonbullous impetigo presents with honey-colored crusts on an erythematous base, typically caused by Staphylococcus aureus and/or Streptococcus pyogenes. Bullous impetigo, due to toxin-producing S. aureus, shows fragile…
Common warts are benign epidermal proliferations caused by cutaneous human papillomaviruses (HPV), most often types 1, 2, 4, 27, and 57. They present as hyperkeratotic papules with thrombosed capillaries (“black dots”). Many resolve spontaneously within 1–2 years, but persistence is…
