What could be the cause of recurring mouth ulcers? I rarely consume acidic foods.

Aphthous ulcers? Aphthous ulcers (whitish, shallow ulders with red rims) are quite common during early/late adulthood. They can be quite painful. The exact cause is not known, but it is believed that an autoimmune process and/or viral infections are causing such. Treatment is usually controlling the symptoms, as they will resolve. Also, possible herpes stomatitis, thus consult doc if u r concerned. Good luck.
Ulcers. Proably the most common type are aphthous ulcers. Stress can cause flare ups. Also, the detergent in (sodium laureth sulfate)in most toothpastes can cause this. Get a brand that specifies that it is sls free. Rarely, more serious disease can cause ulcers therefore its good to get checked by ent. Treatment acutely can involve chemical cautery, anesthetic medications, steroids.