The illness - which is common in March and April - can be identified by a pink rash, sore throat, fever and headaches.
According to Public Health England (PHE), nearly 40 cases of the condition have been reported in the south west of the country since last week.
The infection, which commonly affects young children, generally responds to a course of antibiotics and clears up within a week - but may lead to complications if left untreated.
Dr Theresa Lamagni, head of streptococcal infection surveillance at PHE, said: “Individuals who think they or their child may have scarlet fever should see their GP without delay as antibiotic treatment is needed.
“As scarlet fever is highly contagious, children or adults diagnosed with it are advised to stay at home until at least 24 hours after the start of antibiotic treatment to avoid passing on the infection.”
She reinforced the importance of good hand hygiene at home and at school to tackle the illness.