An allergic reaction occurs when the body misreads something that's typically harmless as being dangerous, explains Kevin McGrath, MD, spokesperson for the American College of Allergy, Asthma, and Immunology. "The immune system creates special white blood cells, called antibodies, to defend against this apparent threat similarly to how it would fight an infection or illness," he says. (That's where symptoms like swelling, itching, runny nose, and wheezing come in.)
People must be born with a genetic predisposition to allergies, but scientists don't know exactly why or how they become allergic to specific things. And while many allergens are quite common, others are much rarer. Here are some of the more interesting cases allergists have seen in their practice, and what you can do if you're affected.
Inexpensive silver-colored jewelry is often made with nickel—one of the most common causes of an itchy rash known as allergic contact dermatitis. About 17% of women and 3% of men have a nickel allergy, says Dr. McGrath; the gender difference is largely due to the fact that women have more exposure to nickel through jewelry (especially piercings), which raises their risk of becoming sensitized.
Switching to high-quality sterling silver or 14-karat gold jewelry usually solves this problem, says Dr. McGrath, although he has heard of very rare allergic reactions to gold, as well. "When people wear a lot of gold jewelry and a lot of makeup, the chemicals in the makeup can actually break down the gold and cause reactions with the skin." For these people, he says, platinum is the best bet.
Cell phones and tablets
People with metal allergies may have trouble using cellular phones, PDAs, and tablet devices, (including iPhones and iPads), as these products often contain potential allergens nickel and cobalt. "People can get rashes on their face, ears, and hands, and irritation in the eyes if they touch their phone and then touch their eyes," says Dr. McGrath.
Once you have a metal allergy, you're sensitive to it for life. But most people are able to safely use these devices as long as they're covered with a protective case—as long as the case itself contains no metal, of course.
Nickel strikes again, this time on your clothing. "The button on the waist of jeans and other pants is usually nickel," says Dr. McGrath. "For people who wear low-rise underwear, that metal can be exposed directly on the skin and cause a little circular red rash."
Wearing a layer between your pants and your skin (like tucking in your shirt) can help, he says; so can painting over the back of the button with clear nail polish. If you do realize you're sensitive to the nickel in your jeans, watch out for it in eyeglass frames, watches, coins, and zippers.
We know, wool is itchy. But some people who are sensitized to lanolin—a natural wax-like substance produced by sheep—can react even more strongly to apparel and blankets made with wool.
Lanolin is also used in some cosmetics, lip balms, shampoos, and ointments. People with a sensitivity to this ingredient should look for items that are labeled lanolin-free.
Flea market furniture
If you have a known allergy to dust or mold, be careful what items you bring into your home—especially if you don't know their history or what could be lurking inside them. "Non-washable fabrics, upholstered furniture, and carpets can all harbor dust mites and mold spores," says Donna S. Hummell, MD, medical director of the Vanderbilt University Asthma, Sinus, and Allergy Program.
Dust and mold are common in most homes already, she adds, but heavily contaminated items can make allergy symptoms worse—or even, in some cases, trigger asthma attacks.
Laundry detergent and dryer sheets
Some ingredients in laundry detergents and fabric softeners—especially dyes and scents—can cause people to break out with contact allergic reactions, says Dr. McGrath. And you don't just have to get the liquid itself on your skin; it can be transferred into the clothes you wear, the towels you use, or the sheets you sleep on.
"We've also seen reactions caused by dryer sheets," Dr. McGrath adds. "Often when people stop using dryer sheets for a while or change up their detergent, their rash goes away."
Averse reactions to strong scents or flavors (like sneezing or coughing after eating hot pepper) are often caused by an irritant effect, rather than a true allergy, says Dr. McGrath. But he does occasionally have patients who develop a true immune-system response to plant-based products like herbs, spices, and essential oils.
"One thing we see is allergic reactions to chamomile tea, because it can cross-react with ragweed," he says. (This means that proteins in chamomile and ragweed are similar enough that allergic people can react to both.) If you have hay fever, you're more likely to experience itchiness, runny nose, or even hives while drinking this herbal tea.
Raw produce and nuts
Cross-reactivity with pollen and grasses can also cause some people to have allergic reactions to raw fruits such as apples, peaches, bananas, melons, and tomatoes. Vegetables like celery, carrots, onions, and potatoes, along with peanuts and hazelnuts, can also cause itchy mouths and inflammation.
"People think that it must be a chemical or something used in the growing process, but it's actually part of the food—not something you can wash off," says Dr. McGrath. The good news? People can almost always eat these items cooked without experiencing symptoms.
People who are allergic to latex can experience an irritating rash when exposed to products—like condoms—made with the plant-based rubber. Some people can even have an immediate, life-threatening reaction called anaphylaxis, which can include difficulty breathing and swallowing.
Fortunately, many items that used to be made with latex (including gloves, hospital equipment, and balloons) are now made with safer materials, says Dr. Hummell. Most condoms still contain latex, but those with an allergy can use synthetic rubber or lambskin alternatives (here's everything you should know about the nine most common types of condoms on the market).
Cosmetics and skin-care products
Chemicals in makeup, lotions, and sunscreens can sometimes cause a rash known as contact dermatitis, which may show up hours or days after exposure. An allergist or a dermatologist may be able to diagnose these types of sensitivities with a procedure called a patch test.
If you know that you're sensitive to certain products, you can also test yourself before using a new formula. "Take a tiny bit and apply it to the same area of skin three days in a row at night before you go to bed," says Dr. Hummell. "If you don't have a rash by the end of the third or fourth day, you're probably going to tolerate it well."
This article originally appeared on Health.com