Although it's not required, having had an allergy when you were younger does make allergies in adulthood more likely. In fact, Dr. Tuck says that even though those childhood allergies may get better over time, you can develop different allergies later in life.Your genetics and family history play a role, too, especially when it comes to what are called "atopic diseases" like asthma, allergic rhinitis, and eczema. "If you have immediate family members with one of those diseases, your likelihood [of developing an allergy] is greater than the general population," explains Dr. Tuck. So, if your dad reacts to ragweed, you're at a higher risk for adult-onset allergies — even if you missed out on 'em on as a kid."Despite what you see on blogs, most adults don't have more than one food allergy," says Dr. Tuck. So, if you grew up with a tree-nut allergy, it's unlikely that you'll develop an allergy to eggs later on. However, within a group of foods, such as fish, people may show " cross-reactivity ," meaning that if they react to tuna, for instance, they may also react to cod. Non-food allergies — including things like hay fever, cats, and drugs — are all still fair game."Your symptoms may seem allergic, but they might not be allergic," says Dr. Tuck. It turns out, there are a fair amount of non-allergy conditions that might look like an allergic reaction. For instance, people with nonallergic rhinopathy often develop a very runny nose after coming in contact with cigarette smoke, air pollution, or perfume. But that doesn't mean they are having a true immune response to those things. That can be especially confusing if you've never had an allergy before.Plus, it can get even more complicated than that. Those who have oral allergy syndrome , for example, develop reactions to certain fruits and vegetables that share proteins in common with things they're allergic to seasonally. So, although that might not be a new allergy, it may mimic one.