Perianal streptococcal dermatitis is the presence of intense perianal erythema with or without scale that is caused by infection with group A beta-hemolytic Streptococci. Group B Streptococci and non-group A or group B Streptococci have also been reported in some cases. It typically occurs between the ages of 6 months and 10 years. It has been rarely reported in adults. Some studies indicate a male predilection.

It can occur in children with streptococcal pharyngitis, but in healthy children, gastric acid should eliminate most of the swallowed pharyngeal bacteria. Digital contamination from an infected site, such as the pharynx or skin, may be the source. Intrafamilial spread is thought to be due to communal bathing or direct contamination. Diapering by a caregiver with streptococcal pharyngitis or carriage may also cause transfer of the infective organism.

In susceptible patients, perianal streptococcal infection can trigger classic, inverse, or guttate psoriasis. In one report, 11% of patients with perianal streptococcal dermatitis also presented with psoriasis.