It's not your imagination. A growing number of adults and children in New Jersey are developing allergies, at all times of the year, even in the dead of winter when there's snow on the ground. 

Who are more New Jerseyans developing allergies? (Dimitri Zimmer, ThinkStock)

"Over the past 25 years, the number of individuals who skin-test positive and are sensitive to things has doubled, and during that same period of time, we've analyzed the things they were allergic to, and it used to be one or two items, now that's four or six items," said allergy expert Dr. Leonard Bielory.

So what is causing this?

Dr. Bielory said there is evidence that modern life may be too clean, and our immune systems aren't coming in contact with as many allergens, so we can't fight them off properly when we do get exposed.

"When many United States citizens were living on farms, allergies were not as prevalent," he said. "It appears the more sterile the environment you put a child in the beginning of life, the more chances that they are allergic later in life."

He said this makes sense, in the same way that we know that it's important to have probiotics -- certain types of bacteria -- in our intestinal system.

The lesson to be learned, Bielory said, might be "let the kids play in daycare, let them catch the common cold earlier in life and other disorders that they get from others, because their immune systems are built on that, it's like a vaccine."

He said at this point, we still don't know what bacteria, and how much of it, is beneficial to the development of our immune systems, but research is ongoing.

He also said besides the hygienic process, there are other factors that affect allergic reaction, including exposure to chemicals in the environment, your own genetic makeup, and what kind of food you eat.

All of these things taken together, Bielory said, is raising the percentage of people with allergies.

"It used to be about 10 percent of the population. Then we saw the number go to 20 percent, now we're reaching between 30 and 40 percent," he said. "But still there's a subset that will probably never develop allergies in general because they don't have their own genetic disposition to do so."