Apple cider vinegar is generally safe in small amounts for most people, but several groups face real health risks from drinking it. If you have gastroparesis, chronic kidney disease, low potassium levels, or take certain medications, apple cider vinegar can make your condition worse. Even healthy people can run into problems with their teeth, throat, or skin if they use it incorrectly.
People With Gastroparesis or Slow Digestion
Gastroparesis is a condition where your stomach empties food more slowly than normal. Apple cider vinegar slows gastric emptying even further, which is the opposite of what you need. A study in BMC Gastroenterology tested this directly in people with type 1 diabetes and gastroparesis. After a meal that included vinegar, the stomach emptied significantly less food compared to the same meal without vinegar. One participant spontaneously reported more frequent episodes of dangerously low blood sugar during a two-week period of drinking apple cider vinegar daily.
This matters because slower digestion throws off the timing of blood sugar changes relative to insulin doses. If food sits in the stomach longer than expected, insulin can peak before glucose arrives in the bloodstream, causing a drop in blood sugar. For anyone already dealing with unpredictable digestion, adding vinegar makes an already difficult condition harder to manage.
People With Chronic Kidney Disease
Your kidneys are responsible for filtering acid out of your blood and maintaining your body’s pH balance. When kidney function is impaired, that filtering system can’t keep up. Apple cider vinegar adds an extra acid load that healthy kidneys handle easily but damaged kidneys may not. UChicago Medicine specifically notes that people with chronic kidney disease may not be able to process the excess acid that comes with drinking apple cider vinegar. If you have any stage of kidney disease, this is one to skip entirely.
People Taking Insulin or Diuretics
Apple cider vinegar lowers blood sugar. A meta-analysis of seven controlled trials found that it significantly reduced fasting blood sugar by about 22 mg/dL on average and lowered HbA1c (a marker of long-term blood sugar control) in people with type 2 diabetes. Each additional 1 mL per day of vinegar was associated with a further 1.25 mg/dL drop in fasting blood sugar. That blood sugar lowering effect can stack on top of insulin or other diabetes medications, increasing the risk of hypoglycemia. If you use insulin, adding vinegar without adjusting your dose or monitoring more frequently is risky.
Diuretics, particularly the potassium-wasting type commonly prescribed for high blood pressure, pose a different problem. Apple cider vinegar consumed in large amounts can lower potassium levels on its own. Combined with a medication that also depletes potassium, the result can be hypokalemia, a condition where potassium drops low enough to cause muscle weakness, cramping, and heart rhythm disturbances. A published case report documented hypokalemia, elevated renin levels, and osteoporosis in a patient who had been consuming large quantities of cider vinegar over time.
People With Acid Reflux or Esophageal Issues
Apple cider vinegar contains 4 to 8 percent acetic acid. Drinking it undiluted, or even poorly diluted, can irritate or burn the lining of your esophagus. Consuming more than one to two tablespoons per day increases the risk of esophageal irritation. If you already have gastroesophageal reflux disease (GERD), esophagitis, or ulcers, the added acid can worsen inflammation and pain in tissues that are already damaged.
Dental Erosion Risk
This one applies to almost everyone who drinks it regularly, but especially to people who already have weakened or thin enamel. An eight-week clinical trial had participants drink two tablespoons of vinegar diluted in a cup of water twice daily with meals. By the end of the study, dental erosion scores increased by 18 percent in the vinegar group, while the control group showed no change. That’s a measurable loss of enamel in just two months, even with dilution and mealtime consumption, which are the standard precautions people recommend.
If you have a history of cavities, sensitive teeth, or enamel erosion, regular vinegar consumption will accelerate the damage. Drinking through a straw and rinsing your mouth with plain water afterward can reduce contact with your teeth, but it won’t eliminate the risk entirely.
Pregnant Women and Immunocompromised People
Many popular apple cider vinegar brands are sold unpasteurized, often marketed as “raw” or “with the mother.” Unpasteurized juices and ciders carry a risk of harboring harmful bacteria, including E. coli. FoodSafety.gov lists unpasteurized juice and cider among the beverages pregnant women should avoid because of documented outbreaks of foodborne illness. The same risk applies to anyone with a weakened immune system, whether from chemotherapy, organ transplantation, HIV, or other conditions. If you fall into either group and still want to use apple cider vinegar, choose a pasteurized version.
Topical Use on Skin
Apple cider vinegar applied directly to the skin can cause chemical burns, particularly when left on for extended periods or covered with a bandage. A case report in The Journal of Clinical and Aesthetic Dermatology described a 14-year-old who applied apple cider vinegar to moles on her nose for three days under bandages. She developed significant redness by the second day and was left with open erosions that carried risks of scarring and permanent pigment changes. The acetic acid in common vinegars, at 4 to 8 percent concentration, is strong enough to erode skin, and occlusion (covering the area) intensifies the damage. Anyone with broken skin, eczema, or other skin conditions should avoid applying it directly.
Safer Ways to Use It
For people who don’t fall into the groups above, keeping intake to one to two tablespoons per day is the standard guidance. Diluting one tablespoon in a full cup of water and splitting it across three meals reduces the concentration your teeth, throat, and stomach encounter at any one time. Using it as a salad dressing mixed with oil is another way to get it into your diet without the direct acid exposure that comes from drinking it straight. Never drink it undiluted, and avoid taking it right before lying down, since that keeps acid in contact with your esophagus longer.