The most common cause of red patches on the tongue is a condition known as geographic tongue. People affected by this condition usually have painless tongue red patches contrasting with areas of gray, giving the appearance of a geographic map. The red patches appear in areas where tongue papillae, the small bumps on the surface of the tongue, have been lost. It appears that these tiny bumps literally fall off of the surface of the tongue leaving red patches behind.
at 2:05 PM on Sep. 27, 2009
The exact cause of geographic tongue isn't completely understood, but there appears to be some genetic susceptibility to this strange condition since it's seen more frequently in certain families. It's also more common in people who have allergic conditions, asthma, psoriasis, and eczema of the skin. It's thought that their may be a hormonal component to geographic tongue since it's significantly more common in women and often makes its appearance during pregnancy and times when hormone levels are fluctuating. How common is this condition overall? It's estimated that around two percent of the population is affected by geographic tongue.
at 2:06 PM on Sep. 27, 2009
It could be a canker sore. More information would be helpful in determining what it is, his age, spot's size, his diet, if it's painful or affects his ability to eat or drink, etc. But if you're concerned, just take him to the Dr. You can also try putting the info into the Symptom Checker on WebMd.com