According to Living Healthy 360, an infected tongue piercing is painful and swollen with some reddening or discoloration appearing around the site of the piercing. It is very sensitive to the touch and may produce some lumps on the tongue.
Living Healthy 360 explains that swelling, pain, and discoloration are the most common signs of infection. Other signs include bad breath and swollen gums. Anyone who believes his tongue piercing is infected should have it treated immediately. Infections can be very dangerous, and oral infections are especially so as they have a greater chance of spreading to the brain. Tongue piercings are more prone to infection than other piercings because the mouth easily accumulates bacteria.
Delta Dental points out that, as with most piercings, tongue piercings should be cleaned and maintained regularly.