Similar symptoms plague people who have what is called perennial allergic rhinitis, a year-round form triggered not by pollen but by sensitivity to pet hair or dander, mold, dust mites or cockroach droppings, among others. All told, an estimated 50 million Americans have some type of allergy, according to the Asthma and Allergy Foundation of America. Additional common allergens that trigger allergic reactions include bee stings, peanuts, seafood, dairy products, eggs, latex, cosmetics, antibiotics, laundry detergents and some pesticides. While some allergies can be life threatening — such as to insect stings or to some foods — that’s rarely the case with hay fever. While the best approach to spring allergies is avoiding pollen, that may be becoming a bit more difficult. A recent study suggests that, at least in the northern hemisphere, “the ongoing increase in temperature extremes” is contributing to a longer pollen season and more pollen overall.