SSTIs involve microbial invasion of the skin, subcutaneous tissue, fascia, or muscle, mainly caused by bacteria and less commonly by viruses, fungi, or parasites. They may spread through lymphatic or hematogenous routes and are classified based on infection depth — superficial (impetigo, erysipelas, folliculitis, furuncles, carbuncles), intermediate (cellulitis), or deep (abscesses, fasciitis, myonecrosis).
SSTIs represent a significant cause of hospitalization and morbidity, with presentations ranging from mild infections such as impetigo to severe, life-threatening conditions like necrotizing fasciitis.