If you've got a rash or a persistent cough, you can call that an ailment. Some other common ailments are allergies or chronic headaches. They can be a real pain. Literally.
The word ailment comes from the Old English eglan meaning "to trouble, plague, afflict," and the suffix -ment from the Latin mentum, which when added to the end of word describing an action turns that word into the result of that action. So the result of something that troubles, plagues or afflicts you is an ailment — a pain or discomfort that just doesn't seem to go away.
