Four of the five people in Keith Patridge's family suffer from environmental allergies. His wife, Melissa, has asthma, as does one of their sons, and another son has food allergies.

Patridge himself, 44, developed allergies as an adult - and found little that could keep them in check.

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"Twelve years ago, it was very difficult to find products that help people to control their environment and keep allergies under control," said Patridge, who started his own store and catalog, Allergy Free Living in Concordville, to provide allergic people with gear.

It's a big market: The Asthma and Allergy Foundation of America estimates that 50 million Americans have some type of allergies: environmental (indoor/outdoor), food and drug, latex, insect, skin or eye allergies.

And when it comes to allergies, the Philadelphia area is above average, ranking No. 33 on the allergy foundation's 2007 list of "The Most Challenging Places to Live With Spring Allergies" (the No. 1 place is Tulsa, Okla.). Here, our pollen score exceeds the average of 150 grains per cubic inch of air daily, and each allergic patient uses about 2.3 medications, prescribed by one of the 4.2 board-certified allergists we have for every 10,000 patients.

That's a lot of sufferers - and so it makes sense that more people are treating allergies as more than a seasonal inconvenience. Instead, they are creating entire hypoallergenic lifestyles.

Patridge's store caters to the trend. Dust mites would have to be awfully brave to enter, as the right half of the store is devoted to eliminating the sneeze-provoking creatures. A number of high-end vacuums, including six brightly colored Dyson models, are opposite a leather sofa (dust mites can't penetrate the leather). The air inside the store, filtered through at least a half-dozen purifiers, is perfectly dry; dampness encourages mold, a common allergen.

More than 6,000 physicians refer patients to the store and associated catalog, and Patridge grosses several million annually. "Typically, we tell people to focus on the bedroom first," he said. "If you can clean your bedroom, get your bedroom under control, you won't be exposed to allergens during the eight, nine hours of the day you spend in your bed."

While Allergy Free Living concerns itself with household products, a large sector of the allergy product market involves food. Eight foods are responsible for 90 percent of food-allergy reactions, according to the foundation: milk, soy, eggs, wheat, peanuts, tree nuts, fish and shellfish.

Most people think of peanut allergies when they think of anaphylaxis, a rare and severe allergic reaction that can lead to a drop in blood pressure, swollen airways, and death. However, milk and egg allergies are more common than peanut allergies, and a food-allergic person can have a reaction from ingesting any food allergen - not just peanuts.

To help people cope, there's a national magazine, Living Without, a "lifestyle guide for people with allergies and food sensitivities," available at Whole Foods. A recent issue includes a piece on visiting Disney parks with a food-allergic child, an article about a submariner who switched to shore duty after being diagnosed with food allergies, and recipes for egg-free, milk-free scones. A full-page ad advertises "Enjoy Life" cookies, which are milk- and egg-free.

These cookies are a favorite of 2-year-old Clara Kantorcyzk of Radnor. Her mother, Jean Kintisch, leads a support group called FEAST: Food and Environmental Allergy Support Team. The group, which has about 40 members, meets monthly at the Memorial Library of Radnor Township.

Kintisch got involved in the hypoallergenic lifestyle when Clara, at 3 months, developed terrible eczema on her face. Once the doctor diagnosed the baby with allergies to milk, eggs, peanuts and tree nuts, Kintisch eliminated allergens from her own diet while she was breast-feeding, and the eczema went away.

Now, Clara enjoys cookies like most kids - but her snickerdoodles are made without milk or eggs. The family doesn't bring nuts (or peanut butter) into the house, and everyone tries to be diligent about washing their hands and avoiding cross-contamination of foods in the kitchen.

"People who are anaphylactic don't know until it happens," Kintisch said. " 'There's only one way to find out - the hard way,' says our allergist."

According to statistics from the Centers for Disease Control and Prevention reported in Child magazine, food-related anaphylaxis caused 12 deaths in 2004, the most recent year for which data is available. This makes the odds of dying from a food-related reaction 1 in 24,471,283; more people died from parachuting, lawn-mower accidents, dog bites, and being struck by lightning. By comparison, vehicle accidents claimed 264,613 lives in 2004.

With food allergies, however, the fear comes in knowing that a life-threatening reaction can happen, not that it will happen.

Some schools have responded to children's food allergies by banning allergens like nuts and nut-related products; others have requested that parents simply refrain from sending peanut products (such as peanut-butter sandwiches) to school. Kids who have food allergies often sit at designated nut-free tables. Nutsafeschools.com offers a downloadable sign for cafeteria tables that reads, "This is a peanut and tree-nut free table."

Allergies are common enough that they have even started to influence fashion. Merion entrepreneur Robin Davison has built a business around food allergies and children's safety. Her company, AllergiK ID, sells bright-red backpacks, rubber bracelets, buttons, and other items marked with an allergy alert.

Davison came up the idea after her 4-year-old son was diagnosed at 11 months old with an allergy to peanuts and tree nuts. "Once he went to camp, we had a really difficult time making sure he was fed food that was safe for him," she said. "For example, once he was almost fed trail mix."

Davison wanted a medical-alert bracelet that would let people know about her son's food allergies, but she was reluctant to get him the standard metal bracelet - it seemed too easy for a kid to use it as a weapon on the playground. So she came up with the idea of red rubber AllergiK ID allergy-alert bracelets.

The red AllergiK ID backpacks are embroidered with the child's name and an AllergiK ID logo. The allergy alert is featured in enormous letters: "peanut allergy," "tree-nut allergy," and so forth.

Some members of FEAST have found that living allergy-free can be alienating.

"The big problem is, not everyone gets it. School, social environment - not even our own families - understand how it can affect them, how difficult it can be. Or how easy," Kintisch says. "A lot of people pooh-pooh it. We feel that it is a big deal: We want to avoid the emergency room."

Part of the anxiety that parents feel stems from the fact that current tests can't predict how an allergic person will react to a substance - skin and blood tests are inconclusive. The only way to truly measure the severity of an allergy is through a food challenge under a doctor's supervision - what Kintisch's allergist calls "the hard way" - in which the person is given small, increasing amounts of the food they are allergic to.

Naturally, few parents leap at the idea of a food challenge for their child. It's far easier to avoid a food and hope the child grows out of the allergy (many do by age 10, though it's unclear why).

Newly diagnosed food-allergic patients are given an adrenaline injector (like an Epi-Pen) to keep handy, and are advised to develop an anaphylaxis emergency plan. Food allergy reactions range in severity depending on a person's sensitivity and how much of the allergen they ingest; typical reactions include a runny nose, wheezing, hives, vomiting, a tingling in the mouth, or stomach cramping

Allergist Nicholas Pawlowski, of Children's Hospital of Philadelphia, counsels his patients in rational avoidance: "You're not going to die from touching it or breathing it," Pawlowski advises his patients about their allergy triggers. "You'll only get sick if you eat it."

However, what a doctor sees as common sense - avoidance and emergency planning - can sound scary to a patient. Scary enough to convince a parent that a serious, chronic, but manageable condition like a food allergy is a life-or-death issue worthy of extreme anxiety.

"I know people who don't go to Gymboree or to the playground, don't have babysitters come to the house because they're scared of leaving their kids with someone else," says Kintisch.

"I don't walk on eggshells. I'm conscious, but I don't think my daughter needs to be in a bubble, either. I'm not willing to keep her isolated."