Allergies - 10 Things You Didn't Know

Allergies of every kind, from mold to milk to metal, are becoming increasingly common in the United States. With a sympathetic nod to those of you bracing yourselves against this spring's burgeoning pollen count, here are 10 allergy facts that don't come up as regularly or reliably as seasonal symptoms do.
1. Allergies can give you a shiner. When hay fever strikes, pressure from nasal congestion can be so great that it causes blood vessels in the face to become constricted. The blood can't flow freely and may pool under the eyes. Blood draining back toward the heart, or venous blood, appears blue in color (compared to arterial blood flowing from the heart, which is red) and, when trapped, results in the appearance of an allergic shiner, sometimes known as "black-eye syndrome."
2. Any organ in the body can be affected by allergies. Sufferers of hay fever (allergic rhinitis) will attest that allergies can cause a runny nose, irritated eyes, and an itchy throat. Some allergic reactions can cause the skin to break out in hives or the intestines to cramp, and allergy-induced asthma takes a toll on the lungs.
"These are the common 'end organs' for allergic disease," explains Asriani M. Chiu, M.D., associate professor of allergy and immunology at the Medical College of Wisconsin. "In a severe allergic response, there can be a systemic reaction that affects multiple body systems. A bee sting, for example, can affect the cardiovascular system and send the body into shock." Consequently, any organ could potentially shut down as a result of reduced blood flow. An anaphylactic response affecting the respiratory system is similarly threatening.
In very rare cases, Dr. Chiu notes, an allergy cell called the eosinophil can target and cause isolated damage to an organ like the esophagus or heart. However, when organs such as the liver or kidneys are affected by an allergy, it's far more likely to be the indirect result of a system-wide reaction.
3. It's not pet hair that gets your dander up. Contrary to popular belief, pet hair is not an allergen—though it's still no fun to clean the sheddings of cats and dogs from your wool coat. Rather, it's the particles of pet dander (dead skin), saliva, and urine trapped in the hair, or airborne in your breathing environment, that prompt allergic reaction.
4. "Allergy-addiction syndrome" lacks credibility. Like a drug addict who craves a chemical that's bad for the body, some people claim to have an addiction to foods to which they are allergic. But paradoxical cravings are most likely explained by a typical psychological trick we play on ourselves: We always want something a little more when we know we can't have it. As Dr. Chiu notes, a child with a food allergy will instinctively spit out food that causes her mouth to itch or her lips to swell. Electing to override that natural survival instinct may be a mild form of masochism, but it's not an addiction.
5. The sharp rise in peanut allergies is still not well understood. The rate of peanut allergies in the U.S. has doubled over the past 10 years, currently affecting between 1 and 2 percent of the population. Prevalence in the U.S. may be explained by our method of processing; dry-roasting is not as popular a method in countries where the allergy is less common. Another prevailing theory is the hygiene hypothesis: Now that we're living in an increasingly sterile environment where diseases are eradicated and bacteria vanquished, the immune system may be seizing on harmless foreign antigens—essentially, protecting our system against a false threat.
A new study reverses recent health strategies. Rather than delaying an introduction to peanuts, the research suggests we might increase tolerance by introducing peanuts earlier and more frequently.
6. Black boys are at especially high risk of having food allergies. A March 2009 study showed that black male children are about four times more likely than the rest of the population to be food allergic. The study of more than 8,200 participants found both food sensitivities and food allergies to be highest among blacks, males, and kids—which leaves these kids right in the demographic crosshairs. Prevalence of food allergy is also higher among persons of lower income. Genetic and environmental factors are being researched, but the cause of food allergies and sensitivities is as yet unknown.
7. Eight foods are responsible for 90 percent of all food allergies. The chief offenders: milk, eggs, peanuts, soy, fish, shellfish, tree nuts, and wheat. As Dr. Chiu explains, some make the list because they're prevalent among children, and others because they prompt lifelong reactions. "A child will 'outgrow' some food allergies, notably milk and egg; as the GI system matures, the system gets better at breaking down the proteins in them that cause an adverse reaction. Other foods, such as shellfish, peanuts, and tree nuts, tend to trigger an allergic response even when broken down, so the reactivity is more apt to be lifelong."
8. A link has been drawn between allergies and obesity—but to date the association is controversial. Some research has suggested that food allergies contribute directly or indirectly to obesity. In 2007, one study published in the journal Diabetes found that a high-sugar, high-fat, low-fiber diet caused an immune response of inflammation, in turn leading to increased insulin resistance, which prompts the body to store more fat.
However, the prevailing wisdom is that allergic disease and obesity are each based on a variety of genetic and environmental factors. The research is not yet conclusive enough to establish a causal link between the two.
9. Nickel allergy is a common culprit of contact dermatitis. If your skin is irritated where contact is made with bracelets, rings, earrings, or eyeglasses, it may be due to nickel content in the metal. Reactions to 24-karat gold or other metals used in fine jewelry (such as platinum or titanium) are rare. Trace amounts of nickel in detergent, nail polish, and makeup, or even in buttons and snaps, however, can cause an itchy rash at the site due to metal allergy.
10. The prevalence of allergies continues to increase. According to the American Academy of Allergy Asthma & Immunology, allergies of every kind—inhaled, ingested, contact, or otherwise—are steadily increasing in rate. Allergic diseases currently affect more than one in five Americans, making them the sixth leading cause of chronic disease in the U.S. If you have pollen or mold allergies, you can check daily counts in your area through the National Allergy Bureau.
"It's important to know what's causing a reaction," Dr. Chiu offers in conclusion. "Healthcare providers and allergy specialists can help identify the specific cause so that you can actually avoid what you're allergic to rather than simply treat symptoms with medication."