A cactus prick can produce a reaction that is similar to an allergic or venomous reaction. The small spines from certain types of cacti can become lodged in the skin and cause dermatitis. This can look like an itchy rash or even a granulomatous response on the skin. Infection can also occur which would be treated with antibiotic medications. Removing the spines and cleaning the area thoroughly are the only real remedies other than seeing a dermatologist.