In recent years, pediatrician William Sears, MD, has seen a lot more cases of asthma and eczema in his San Clemente, Calif., office. Dairy and wheat are still the biggest culprits, but experts believe new factors may be contributing to the rise in food sensitivities, including synthetic additives such as partially hydrogenated oils and artificial colors, flavors, and sweeteners, as well as genetically modified ingredients.

Often undiagnosed and untreated, food intolerances can damage tissue over time, warns Sears, author of The N.D.D. Book (Little, Brown, 2009), a book that addresses what he calls nutrient deficit disorder. Increasingly, kids are developing what used to be adult-onset diseases, such as type 2 diabetes, obesity, depression, cardiovascular disease, and acid reflux, he says.

If you think your child may be reacting to something in his or her diet, the first step is to look for clues. “A lot of parents already suspect the answer,” says Kelly Dorfman, LND, author of What’s Eating Your Child? (Workman, 2011). Become a “nutrition detective,” she suggests, noting when and how possible symptoms arise. Here’s a guide to assessing the evidence and finding solutions.

1. Spitting up

Possible culprit: Intolerance to casein, a dairy protein. Casein in dairy products—which is different from the casein in human milk—that gets into breast milk or is in formula can irritate an infant’s gut lining, causing gastroesophageal reflux disease (GERD). Later, the symptoms may morph into chronic ear infections or constipation, says Dorfman.

Action plan: Remove dairy from the baby’s and nursing mom’s diet for at least a week. (It takes four to five days for dairy to clear from breast milk.) For formula-fed infants, choose a brand made with predigested casein or whey. To heal baby’s damaged intestinal lining, give 10 billion CFU daily of probiotic bacteria mixed in a bottle or sprinkled on solid food.

2. Chronic diarrhea

Possible culprit: Intolerance to gluten (a protein in wheat and other grains) or lactose (dairy sugar). Diarrhea is the gastrointestinal tract’s way of getting rid of problematic substances. Therefore, the most common symptoms of both gluten and lactose intolerance are diarrhea, gas, and bloating.

Lactose intolerance is usually the root cause because the enzyme that digests lactose (lactase) is easily inactivated when the gut is irritated. When you’re gluten sensitive, digesting gluten irritates the gut, so almost everyone with gluten intolerance also cannot tolerate lactose, Dorfman says. Thankfully, fermented dairy products such as cheese and yogurt have low lactose levels, so consuming them is often safe.

Action plan: Get a blood test to rule out celiac disease; then eliminate gluten for at least a month. Although the diarrhea could resolve within a week, it may take a few weeks to get a clear picture with school-aged children. “The birthday parties, the grandma visit—there’s often something that causes accidental cheating,” Dorfman says. “You need a longer period to see a trend.”

3. Chronic ear infections

Possible culprit: Dairy intolerance and, for some, soy sensitivity. Some research has shown that 90 percent of kids with recurring ear infections or ear fluid have food reactions, a statistic Dorfman says her current patients corroborate. The usual suspect: dairy products. However, about half of people who react to dairy also react to soy, according to Dorfman.

Action plan: Quit dairy and soy for several months. Because children don’t suffer ear infections every week, it can take longer to verify a correlation. Dorfman recommends eliminating soy milk, soy yogurt, and tofu, but adds that ultrasensitive individuals may need to avoid processed foods, most of which contain soy byproducts.

4. Eczema or itchy skin rash

Possible culprit: Reaction to a combination of gluten, casein (in dairy products), eggs and what Dorfman calls “extended” citrus (oranges, grapefruit, tangerines, lemons, strawberries and pineapple).

Action plan: Ask an allergist to conduct an IgE radioallergosorbent (RAST) blood test on your child. Because an itchy rash suggests a histamine response, blood tests can be more accurate here than they can be in detecting food sensitivities.

5. Hyperactivity

Possible culprit: Sensitivity to artificial colors, or even sugar. According to Sears, children’s underdeveloped blood-brain barrier makes them more vulnerable to the neurotoxic effects of chemical food additives, such as artificial colors and monosodium glutamate (MSG).

A 2007 British study linked six food colors with possible hyperactivity in children. As a result, the European Union now requires most foods containing artificial food dyes to carry a warning label. Thus far, the FDA has not issued a similar ban or required additional product labeling. Also watch sugar intake; some kids are literally hypersensitive to the sweet stuff.

Action plan: Buy organic; by definition, organic products are certified to contain no artificial colors. If organic options aren’t available, scrutinize food labels for the nine petroleum-based synthetic dyes currently approved for food use in the United States: Blue 1 and 2, Citrus Red 2, Green 3, Orange B, Red 3 and 40, Yellow 5 and 6. To avoid added sugars, look beyond the Nutrition Facts panel, which combines natural and added sugars for a total amount, to the ingredients list. Words like high-fructose corn syrup, sucrose, glucose, fructose, cane sugar, and syrup indicate added sugars.

6. Crankiness

Possible culprit: Gluten intolerance. Gluten sensitivity is traditionally associated exclusively with digestive disturbances, but some studies have recently linked it to neurological symptoms, which can range from moodiness and chronic headaches to ADHD and coordination loss.

Action plan: Eliminate gluten for a month to assess a connection between mood and food. Other reasons may account for kids’ agitation; however, if food is the culprit, says Dorfman, children will often want to eat the problem food excessively.

7. Small stature or picky palate

Possible culprit: Gluten sensitivity or zinc deficiency. Because gluten intolerance interferes with nutrient absorption, suffering kids often fail to thrive. “Small size—height or weight—is a classic symptom of celiac disease,” Dorfman says.

Zinc could be another factor: The mineral normalizes appetite and, through its relationship with growth hormones, helps the body develop. If levels are low enough, a child’s growth will be stunted, perhaps in the fifth percentile or lower for weight and height on the standard growth charts. In this case, a child may rarely be hungry, be a picky eater, or complain that food smells or tastes “funny,” Dorfman says.

Action plan: Eliminate gluten from the diet for a month. Ask your pediatrician for a blood test to determine serum zinc levels, or buy a zinc sulfate taste test online. After sipping a bit of zinc sulfate solution, your child will report tasting nothing (which indicates deficiency) or a bad flavor (no deficiency). Zinc-rich foods include beef, chicken, beans, pumpkin seeds, cashews, and chickpeas. If there’s a deficiency, ask your health care provider about an adequate supplement dose based on your child’s age.

After her son got eczema as a 3-month-old, Nederland, Colorado-based writer Pamela Bond used an elimination diet to confirm that dairy was the culprit.