What Causes Drool Rash On Wrist Of A Baby?

My 5 month old is constantly drooling and chewing on his hand (assumed teething) he started developing a few red bumps on his.chin and.under his mouth (drool rash?) but now the rash is on his wrist too. Could the constant chewing on his hand have caused a drool rash on his wrist or should i be concerned?