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Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue. Clinical features include erythema, warmth, swelling, pain, and systemic signs (fever, leukocytosis) in moderate-to-severe cases. The most common cause is β-hemolytic streptococci (particularly Streptococcus pyogenes). These organisms spread rapidly along superficial lymphatics, producing ill-defined borders. Staphylococcus aureus, especially MRSA, is more associated with purulent skin infections (abscesses, furuncles, carbuncles). Pseudomonas is seen in puncture wounds through shoes or immunocompromised patients. Candida causes cutaneous candidiasis in moist intertriginous areas, but not rapidly spreading cellulitis. Management involves systemic antibiotics (e.g., cephalexin, clindamycin, or vancomycin depending on severity and MRSA risk). Complications include bacteremia, necrotizing fasciitis, and sepsis. Distinguishing erysipelas (well-demarcated, superficial) from cellulitis (deeper, ill-defined) aids diagnosis, but both are streptococcal predominant.