Lactose intolerance is caused by a lack of adequate lactase enzymes in the body to properly digest the sugars found in dairy products. Children can be born with insufficient lactase or adults may develop decreased lactase as they age. Many individuals confuse lactose intolerance with a dairy allergy (or casein allergy), however, patients with dairy allergies are allergic to the protein, or casein, found in foods containing milk. They will often react with hives, itchy skin, skin flushing, and in severe cases, closing of the airways (or anaphylaxis).

The symptoms of lactose intolerance include the following:

1. Stomach ache and bloating
Lactose intolerance leads to stomach pain due to insufficient digestion of the carbohydrate, lactose. Since digestion of the carbohydrates doesn’t occur and there is poor absorption into the small intestines, fermentation occurs and releases an acid, which irritates, leading to stomach pain. The pain can be quite severe, and in cases where lactose is consumed, the pain often becomes unbearable in the lower belly. Apart from stomach cramps, gas may also build up, which leads to bloating.

2. Constipation
Consuming dairy products often causes constipation after consumption. Constipation is often characterized by a hard stool that’s difficult to eliminate. It’s caused by the inability to digest lactose, and the over-production of methane gas, which in turn slows the movement of foods through the gut and bowel during waste elimination.

3. Diarrhea or loose stools
If you are not experiencing constipation, you may suffer from diarrhea or loose stool, which is among the common symptoms of lactose intolerance. Diarrhea with lactose intolerance is caused by an increase in water in the colon. Loose stool is due to this high water content. Diarrhea can become painful over time and may lead to dehydration since you are losing water in large amounts.

4. Headache
Healthline.com reports that fatigue and headache are rarer in patients with lactose intolerance, which may be caused by dehydration if you suffer from diarrhea or loose stools, which can decrease needed water in the body.

5. Mouth ulcers
Mouth ulcers, or canker sores, although rarer symptoms in patients with lactose intolerance, may occur due to digestive issues. Mouth ulcers are more indicative of a mild milk allergy if you suffer no other evident symptoms. If you do experience canker sores after eating dairy, try to eliminate it from the diet to see if there is a difference.

Unfortunately, lactose intolerance is a lifelong ailment that is treated by avoiding dairy products altogether. While some supplements, such as lactase enzyme tablets or drops like Lactaid, can be recommended to break down the lactose as an efficient remedy, most doctors will recommend using alternative dairy products, such as nut, oat, or soy milks, yogurts, and vegan margarines and iced desserts.