According to the Mayo Clinic, a raised, itchy rash on a tattoo usually is the result of an allergic reaction to tattoo ink. Red, green, yellow and blue inks are the most common offenders, but an allergy to any color ink is possible. Allergic reactions can occur immediately or years after getting a tattoo.
Tattoo artists create tattoos by pricking the skin repeatedly with a needle that contains dye. A tattoo breaks the skin, so infection, inflammation, allergic reactions and scarring are always a risk. Allergic reactions typically cause itching, while infections cause pain, redness, swelling and pus-like drainage, the Mayo Clinic explains. Inflammation sometimes manifests as small, painless bumps called granulomas. Deposits of scar tissue, called keloids, also occur around some tattoos.
According to the Metanomicon, proper attention to the kind of ink used in the tattooing process minimizes the risk of allergic reactions. Metal-based inks are particularly allergenic, so request an organic, vegetable-based dye if you are prone to allergies.
Skin reactions are also minimized with proper aftercare of the tattoo. Metanomicon says to wash the area gently with warm, soapy water, and pat it dry with clean paper towels. Use a non-greasy moisturizer, and avoid petroleum jelly, antibiotic ointments or topical antihistamines, such as diphenhydramine spray or hydrocortisone. Within four to six hours, remove the dressing that the tattoo artist applied, and leave the area open to the air. Take showers rather than baths, and don't go swimming until the area is completely healed.