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Lactose Intolerance versus Milk Allergy


More people ask me if Lactose Intolerance (LI) is the same thing as an allergy to milk or dairy products than any other question. They are not the same; they are not even related. Here are the basics on how to tell them apart.

Lactose Intolerance

    People who have LI cannot digest the milk sugar, lactose, because they manufacture too small a quantity of the digestive enzyme, lactase. Too small is a relative term. If you drink only tiny amounts of milk, even a tiny amount of lactase is sufficient. Too much milk (or any dairy product) can overwhelm even a fairly large lactase supply. How much is too much? That depends on a dozen factors, and can be hard to judge, even from meal to meal.

    Undigested lactose sits in the intestines and does two things, both bad. It draws water into your intestines, producing diarrhea, and it gets fermented by the bacteria in your colon, producing gas. That's why the symptoms of LI include, in addition to gas and diarrhea, flatulence, bloating and cramps. Note that these are all symptoms of the lower intestines. Anyone (except for young children) who gets vomiting, burping, heartburn, or other stomach ills, should look for a difference cause.

    Food can take 12 hours to two days to completely pass through your intestines. That's why symptoms can last for a long time and that's why it can be hard to pinpoint exactly which foods are bothering you. Symptoms can also start almost immediately after eating dairy. This is not because the dairy has hit your intestines, but because food in the stomach triggers what is called peristalsis in the intestines, the muscle movements that push food through. If you are already suffering from excess gas and water, you can feel the pressures of diarrhea long before any new food has a chance to leave the stomach.

    LI is a normal part of aging for the vast majority of people around the world, but it can also be caused by anything (disease, drugs, surgery) that damages the intestines. This is called Secondary LI. It can be temporary, clearing up when the disease goes away or the damage heals, or, in adults, especially, it can be permanent.

    Infants, whose intestines are still delicate, are especially vulnerable to Secondary LI. A "stomach flu" or any prolonged bout of diarrhea can knock out their lactase-making ability. They need to be taken off all milk (both breastmilk and milk-based formula) until their intestines can heal. this can be for several weeks. Fortunately, nearly all babies will be able to drink milk normally once healed.

Milk or Dairy Allergy

    A milk or dairy allergy is a reaction to the protein in milk. There are two milk proteins, casein and whey. Some people are allergic only to one or the other. Most are allergic to both. The safest course in either case is to avoid all dairy products.

    This is very different from LI, in which most people can still have small or moderate amounts of milk. What's the difference? An allergy is an immune system reaction. Your immune system fights foreign invaders to the body using what are called antibodies. When these invaders are harmful bacteria or viruses, this is a very good thing. In people with allergies, however, the immune system reacts in the same way to dairy proteins that leak into the bloodstream instead of being properly digested. This can lead to a huge number of possible symptoms.

    And a great deal of confusion. You see, the body contains more than one type of antibody. True allergies are caused (technically, mediated) by Immunoglobulin E (IgE). These are the dangerous ones, the ones that can cause people to get hives all over their bodies, or have trouble breathing, or, in the worst cases, go into anaphylactic shock and die. Fortunately, true allergies are extremely rare, affecting only a percent or two of the population.

    But all those other antibodies can also cause reactions. These are also sometimes called allergic reactions, and this is the source of much of the confusion. (It is only recently that doctors began to understand the differences themselves and so too much of the old and obsolete terminology is still hanging around.) You'll sometimes see references to protein intolerance, even though it is nothing like lactose intolerance. The best name is hypersensitivity.

    No matter what name is goes under, a protein hypersensitivity is easy to confuse with LI. They both are likely to cause problems in the intestines. But in addition to gas and diarrhea, they also can cause vomiting or colic.

    Children are the most likely sufferers of both allergies and hypersensitivities. Even breast-fed babies who have never touched formula can suffer from allergies, because dairy proteins can leak into the mother's milk. And even if this does not happen, they can rapidly develop allergies after their first exposure to milk-based formula or milk itself. (I'm assuming cow's milk, but this is also likely to be true for goat's or any other type of milk.) Most babies will thrive on soy-based formulas or milks, and there are other non-dairy alternatives for those rare few who are also allergic to soy.

    Still confused? Here's a chart to highlight some of the differences in babies. (It sometimes happens that the symptoms first appear in older children or even adults, but the basics of the chart are true for them as well.)

    Dairy Allergy Dairy Hypersensitivity
    Reaction time Immediate
    (within 45 minutes)
    (45 minutes to 20 hours)
    Trigger Trace amounts of protein Moderate to large amounts of protein
    Symptoms Hives, swelling, rashes, coughing, wheezing, shock Gastrointestinal - vomiting, diarrhea, colic
    Skin-prick test Positive Negative
    IgE levels Elevated Normal
    Develops primarily in: Breast-fed babies Formula-fed babies
    Later effects Persists for several years; possibly into adulthood Goes away after infancy


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