What is the yellow spot on my tongue?

Two very different things can look like a yellow spot:

• A yellow ulcer - a small, round or oval sore that stings with salty or acidic food. The yellow is the base of the ulcer, not something sitting on top, so it does not wipe away.
• Yellow coating - a soft film of bacteria, dead cells and food stain, often patchy and thickest at the back of the tongue. It is painless and lifts with a scraper or brush, leaving normal pink tongue underneath. If your whole tongue looks yellowish, read our guide to yellow tongue.

Pain is the quickest clue. A tender spot is almost always an ulcer or an inflamed bump; a painless film is almost always coating.

Canker sores (aphthous ulcers)

MedlinePlus describes a canker sore as a painful open sore that is white or yellow and surrounded by a bright red area. It usually starts as a red spot or bump, then opens into an ulcer, and turns grayer as it heals. Most are under 1 cm across. Pain often eases in 7-10 days, and full healing takes 1-3 weeks. Triggers include biting the tongue, rough brushing, dental work, stress, hormonal changes, food sensitivities and low iron, folic acid or vitamin B12.

Patchy yellow coating

Coating builds up where the tongue is roughest and least disturbed by eating and talking. Dry mouth, mouth breathing, smoking, coffee and illness can all turn it yellow. Because the coating is uneven, it can look like scattered yellow spots rather than a smooth layer.

A healing burn or bite

A small injury from a hot drink, sharp food or biting can become a shallow sore that looks yellowish while it heals, much like a canker sore. It should improve steadily within a week or two.

Lie bumps

Inflamed papillae can look white to pale yellow and sit on the tip or sides. They are sore but usually disappear within a couple of days.

• Thrush: usually white, but in babies the NHS notes the coating can turn yellow or gray. In adults the patches wipe off to leave red spots that may bleed.
• Scarlet fever: the CDC describes a yellowish white coating with red papillae poking through early on, before the tongue turns bright red. It comes with fever, sore throat and a rough rash.
• Recurring ulcers with other symptoms: frequent canker sores can be linked to conditions such as coeliac disease or Crohn's disease, which the NHS lists among causes of multiple mouth ulcers.

• Rinse with salt water (half a teaspoon of salt in warm water) a few times a day.
• Avoid hot, spicy, salty and acidic food and drink until it settles. Drinking cool fluids through a straw can help.
• Use a soft toothbrush and an alcohol-free mouthwash. A toothpaste without sodium lauryl sulfate may reduce irritation.
• A pharmacist can suggest a numbing gel, protective paste or antiseptic rinse for sore ulcers.
• Keep cleaning the rest of your tongue, but skip the sore spot itself until it has healed.

For yellow coating, the fix is mechanical: clean the top of the tongue gently each day, drink enough water, and cut back on things that dry or stain the mouth.

For stubborn or very painful ulcers, a dentist or doctor may prescribe a stronger mouthwash or a steroid treatment. If ulcers keep coming back, they may check blood for iron, folate and B12 levels or look for an underlying gut condition. Any sore that does not heal is examined carefully, because a non-healing ulcer can occasionally be an early sign of mouth cancer.

MedlinePlus advises contacting a provider if a canker sore does not go away after 2 weeks of home care, gets worse, comes back more than two or three times a year, or appears with fever, diarrhea, headache or a skin rash. The NHS advises seeing a GP or dentist for any mouth ulcer that lasts longer than 3 weeks.