Sugar is found in many of the foods you eat. It’s found in fruit and milk, and is added to foods and drinks to give them a sweeter taste. It’s also in most desserts and things like ketchup, salad dressing, and cold medicine.

Sugar is a type of carbohydrate, and it comes in the following forms:

  • Glucose is the body’s main source of energy.
  • Sucroseis table sugar, or the white stuff we spoon into coffee and add to cookie recipes. It contains a mixture of glucose and fructose, and is made from sugar cane or beets.
  • Fructose is sugar from fruit.
  • Lactose is the main sugar in milk and other dairy products.

Some people have an intolerance or even an allergy to certain types of sugar. If you have a sugar allergy, you might experience symptoms after eating it that include:

  • hives
  • stomach cramps
  • vomiting

Some people may experience a severe allergic reaction called anaphylaxis. It can be life-threatening. Symptoms include:

  • shortness of breath
  • swelling of the lips, tongue, or throat
  • wheezing

Intolerance to lactose and other sugars often affects the gastrointestinal (GI) tract. After eating these sugars, you’ll develop symptoms like:

  • bloating
  • gas
  • nausea or vomiting
  • abdominal cramps
  • diarrhea

It’s easy to mistake a food allergy and a food intolerance. Both an allergy and an intolerance can cause you to have symptoms after eating that food.

A food allergy happens when your immune system mistakes the proteins in certain foods for foreign invaders like viruses or bacteria. It launches an attack, triggering the release of chemicals that cause allergy symptoms like hives or shortness of breath.

Only a small number of foods cause most food allergies. Some of these include:

  • peanuts and tree nuts
  • shellfish
  • eggs
  • milk

People who have a milk allergy don’t react to the sugar in milk. They react to a protein in it.

Unlike an allergy, intolerance or sensitivity to sugar doesn’t involve an immune system response. Instead, your body has trouble digesting sugar. For example, people with lactose intolerance can’t digest the lactose in milk.

True sugar allergies are rare. Sugar intolerance is more common, especially lactose intolerance. About 65 percent of people have at least some trouble digesting lactose. This sugar becomes harder to digest as you get older.

Sugar intolerance won’t turn into an allergy. An allergy happens because of an immune system reaction. Intolerance happens because your body has trouble digesting the food.

If you do have a severe allergy to sugar, you can have a dangerous reaction if you eat it. This reaction is called anaphylaxis. It causes symptoms like shortness of breath, wheezing, and swelling of the mouth. Anaphylaxis can be life-threatening if it’s not treated right away.

Learn more: What is a lactose tolerance test? »

People with lactose intolerance lack the enzyme lactase, which breaks down the sugar lactose in dairy products. Because their bodies can’t digest lactose, they have GI symptoms like bloating, gas, and diarrhea. People from the following ethnic groups are more likely to be lactose intolerant:

  • East Asian
  • West African
  • Arab
  • Greek
  • Jewish
  • Italian

Disorders that affect the GI tract can also make it harder for the body to break down sugar. Some people with irritable bowel syndrome (IBS) have digestive symptoms after eating fructose. Children with functional gastrointestinal disorders (FGD) may not digest and absorb lactose and fructose well.

People with celiac disease can have trouble eating sugar, too. People with this disorder can’t eat gluten. Their immune systems react to the protein gluten, which is found in wheat and other grains. When they eat gluten, their bodies launch attacks that damage the intestines. Their bodies may also have trouble breaking down carbohydrates, including sugars like lactose and fructose.

If you suspect you might have a sugar allergy, see an allergist. Your doctor can diagnose an allergy with a skin prick or blood test. A breath test can determine whether you’re lactose intolerant.

Learn more: The effects of anaphylaxis on the body »

Depending on how severe your response is to sugar, you may have to avoid or limit foods that contain it. If you’re lactose intolerant, you’ll need to cut back on dairy or avoid it.

If you have a severe sugar allergy, carry an auto-injector wherever you go. This device delivers a dose of the hormone epinephrine to stop the reaction. The shot should relieve symptoms like shortness of breath and swelling of the face.

If you’re allergic to sugar, you’ll need to avoid anything that contains it, including:

  • soft drinks and fruit juices
  • syrup, jams, and jellies
  • desserts, such as cookies, candy, ice cream, cake, and candy bars
  • cereals, granola bars, crackers, and bread
  • peanut butter

Other sweeteners that contain sugar will be off-limits, too. You’ll want to avoid:

  • honey
  • cane juice
  • agave
  • molasses

If you’re lactose intolerant, stay away from these dairy foods:

  • milk and cream
  • butter
  • cheese
  • ice cream, sherbet
  • pudding
  • cream soups and sauces
  • yogurt

Also watch for hidden sources of sugar. Sometimes it’s added to foods you’d never expect, like:

  • salad dressing
  • barbecue sauce
  • pasta sauce
  • ketchup
  • some medicines

If you need to cut back on or avoid sugar, try one of these sugar substitutes to sweeten your foods:

  • aspartame (Equal, NutraSweet)
  • saccharin (Sweet‘N Low)
  • sucralose (Splenda)
  • stevia

You can still enjoy dairy if you have lactose intolerance. Just switch to lactose-free milk, ice cream, and other dairy products. You can also buy lactase tablets over the counter. These tablets contain the lactase enzyme to help your body digest lactose.

A sugar allergy is rare. But you may have an intolerance. If you have lactose intolerance, your symptoms may get worse as you get older.

You can maintain food allergies and intolerances by monitoring your diet. Let people know that you can’t eat sugar.

There are many sugar substitutes you can try. Experiment until you find options that fit your tastes.