It's safe to say you should avoid any substance that causes allergic reactions for millions of people. But mass amounts of common allergens are piling up around us all the time. Whether they're lurking inside your bed, just out the window, or in plain sight, it’s important to know your enemy through and through.

While these 4 allergen facts may not be particularly "fun," they will be helpful to arm yourself against allergens both inside and outside of your home!

1. Threatening Thunderstorms

Rain is often good for allergy sufferers, as it clears pollen out of the air.But there’s a reason April showers give you just as many allergy symptoms as May flowers. Thunderstorms can rip mold and pollen cells apart—wreaking havoc on your respiratory system.

2. Invisible Roommates

A popular rumor even suggests that your mattress could double in weight over the course of 10 years due to the collection of allergens. While that may not be entirely true, according to materials published by Ohio State University, a typical used mattress may have 100,000 to 10 million mites inside.

Worse still, 10% of the weight of a two-year-old pillow can be composed of dead mites and their droppings. Dust mites love pillows. Your pillow is an ideal breeding ground for millions of dust mites—an allergy for about 20 million Americans according to the Asthma and Allergy Foundation of America.

3. Worst Allergy Season Ever

You’re not imagining it—pollen season really is longer than it used to be. Increased carbon dioxide in the atmosphere drives the plant reproductive cycle, leading to the production of more pollen. According to one study, the ragweed season has extended 13 to 27 days longer across the U.S. since 1995.

4. Mold On Mold On Mold

Many different types of mold cause allergic reactions and can thrive in both indoor and outdoor environments. Luckily, most of them only cause problems during certain times of the year.

In colder climates, they can be found outside from late winter through the early fall months. In warmer climates, spores can survive throughout the entire year, but the highest levels are found from late summer to early fall. While indoor molds can occur year round, indoor mold levels are  generally higher when outdoor mold levels are higher. Although indoor mold contamination can be a problem, one of the most common sources is from the outside environment.

But don’t let any of this drag you down too much this allergy season. To combat these less-than-exciting bits of information, here is one reasonably fun fact: using bedding with allergen barrier fabric prevents allergens from collecting in your home, leaving you with a more restful night’s sleep.