The two most common causes of feeling ill after eating bananas are latex sensitivity and eating too quickly. Doctors often recommend bananas to patients recovering from stomach illnesses because they are soft, mild and easy to eat. When eaten too often or too quickly, however, they irritate sensitive stomachs. Inadequate chewing of under-ripe bananas exacerbates this problem.
Bananas are also distant relatives of the rubber tree, the source of latex. Individuals who are sensitive or allergic to latex occasionally develop an aversion to bananas. Chestnuts, kiwis and avocados are also distantly related to the rubber tree and are potentially problematic for people with latex allergies. The Better Health Channel of the State Government of Victoria, Australia, states that allergies to plums, strawberries and tomatoes also result from latex allergies.
According to WebMD, individuals with asthma, eczema and urinary tract problems have a predisposition to developing a latex allergy. Medical professionals, people who work in the rubber industry and those who frequently use latex condoms also develop latex allergies more frequently than the rest of the population. The Better Health Channel explains that 10 percent of health care workers eventually develop a sensitivity to latex. Individuals who experience stomach pain after eating bananas and who meet the aforementioned criteria often learn that latex is the root of their problems.