No side effects are generally known or expected to occur with apple fruit. However, apple seeds should not be eaten, as they contain cyanide and are poisonous. Eating large quantities of the seeds can cause death. There is however, hope here because chances that one will consume large amounts of apple seeds are relatively low.  When one eats the seeds, the cynide is released in the stomach as the seeds are digested, so it may take several hours for the symptoms of poisoning to appear.  Apple may cause an allergic reaction in people who are sensitive to the Rosaceae family. Fruits which belong to the Rosaceae family include apricot, almond, plum, peach, pear, and strawberry. If one is allergic to any of these fruits it would be advisable to consult with a health professional before taking apples.

Drinking too much apple juice may trigger diarrhea, as apples and apple juice contain sorbitol, a naturally occurring but undigestible sugar. Some artificially sweetened apple juice may contain chemical sorbitol as well. If one has a tendency to develop kidney stones, apple juice should be avoided as it contains oxalates, which may trigger the formation of calcium oxalate stones.

Apple cider vinegar is often taken as a natural supplement which provides many potential health benefits. However, if taken in excessive doses or over a prolonged period of time, some side effects are bound to occur.

Vinegar is very acidic, making it damaging to teeth enamel, particularly if consumed undiluted. Frequent taking of apple cider vinegar may weaken the tooth enamel. To prevent this, vinegar should be diluted with water or drunk through a straw to limit contact with teeth. One should also rinse the mouth with fresh water to remove the acid from teeth.

Excessive consumption of apple cider vinegar could lead to low blood potassium levels (hypokalemia) and low bone density. Therefore, one should stick to low doses of apple cider vinegar or avoid it altogether if one has osteoporosis or taking potassium-lowering medications.

Excessive doses of apple cider vinegar have been found to cause damage to skin and throat. To prevent this, one should always dilute the vinegar with water before drinking or applying to the skin. It is safer to take liquid vinegar instead of pills.

Some people experience an allergic reaction to vinegar, including symptoms such as swelling, hives and difficulty in breathing. Apple cider vinegar may aggravate indigestion and heartburn. It is advisable to consult with your doctor before you start taking heart medication, diuretics, prescription laxatives and insulin.