How long do allergies last—a few years or your whole life?

If we were to sum up allergies with an emoji, it’d be a shrug. We know so little about them, and yet tens of millions of Americans experience allergies of some kind or another throughout their lives. They come. They go. They evolve slowly or shift rapidly. Perhaps the only constant is that they’re becoming more common.

But there is some positive news for allergy sufferers everywhere.

“The only good thing about getting older is that​,​ in many cases, allergies are less prevalent,” says Clifford Bassett, medical director of Allergy & Asthma Care of NY and an allergy specialist at New York University. Changes inside and outside our bodies as we age affect the way we react to potential irritants from ragweed to crab to dogs. Why? Well, that’s a little more complicated, and there’s more than one possible reason that your allergy status just switched.

You outgrew your childhood food allergies

Around 60 to 80 percent of kids with milk and egg allergies outgrow them by age 16. Only 20 percent of kids with peanut allergies do so, and only 14 percent of those allergic to tree nuts. Just 4 or 5 percent outgrow a shellfish allergy.

Why? Unfortunately, the answer is that we mostly have no idea. We know some general associations—the earlier a child has an adverse reaction to food, the more like they are to outgrow it—but scientists don’t yet understand why some kids age out of their reactions and others don’t. We do know that early exposure to small amounts of food allergens, especially peanuts, helps prevent allergies in the first place. But we have no idea how to actively reverse them once they happen. If you get allergies as a kid, you just have to wait and see if your tolerances change in the future.

[Related: These are the most common allergies (and the deadliest).]

One of the few things researchers have observed is that there does seem to be a time limit to ridding yourself of childhood allergies—if you haven’t outgrown an allergy by your teens, you’re likely to have it for life.

A new place means potential new allergy symptoms

Allergies, especially the seasonal variety, can change a lot over a lifetime, but it might not have anything to do with your body. Every place you live has its own set of allergens, so moving from one town to the next will likely change your allergies too. Teens moving out of their parents’ houses or adults changing jobs may experience a sudden surge of allergies, or sweet, sneeze-less relief.

It also takes time to become allergic to things. You may not feel a reaction to ragweed during your first summer in Tennessee, but have a full-blown allergy the next. That’s because you became sensitized one year and reacted the next. Similarly, you may visit someone with a dog and seem fine, but sneeze constantly the next time you hang out at their home.

You’re just allergy-prone

Some people are just unlucky. Again, we have no idea why, but clearly, a subset of humans have immune systems primed to identify allergens as potential dangers, giving those poor folks a whole host of allergies while others go sneeze-free. People with one allergy are far more likely to develop another, and as far as we can tell there’s no way to avoid that unless you prevent exposure altogether. And since most of us don’t want to live in bubbles, that means allergy-prone folks are likely to suffer the sniffles their whole lives.

This is distinct, however, from atopy. Atopy is a genetic predisposition to acquiring allergies that essentially means that nearly everything you come in contact with allergen-wise will become a full-blown allergy. Getting a dog? You’ll be allergic soon. Moving house? Enjoy the new outdoor allergies. Atopic people are also more likely to have eczema and asthma. Corticosteroids can sometimes help, as can allergy shots, but it’s still often a lifelong affliction.

As our body changes, so do our allergies

The link between hormones and allergies hasn’t been well studied, but some small studies and anecdotal evidence suggest that your immune system can shift a bit in response to hormonal changes. Like nearly everything hormone-related, this affects people with menstrual cycles the most. “In women, the effect of hormones​,​ such as estrogen​,​ may lead to ​a ​worsening of their asthma during different​ times of the menstrual cycle,” explains Bassett. Puberty, pregnancy, and menopause are also common times of allergic change—at least anecdotally, since few studies on the subject exist in the literature. Asthma symptoms definitely change during these shifts in hormonal balance, and female bodies experience more autoimmune diseases and immune responses generally, which seems to indicate that female sex hormones have a significant influence on the immune system.

[Related: Half of the people who think they have food allergies actually don’t.]

Bassett also notes that factors like weight gain and obesity can affect your immune system, leading to less well-controlled asthma and other allergy symptoms over time. Older adults also tend to have a drop off in the kind of antibodies that instigate allergic responses, which means they may lose their reaction to a food or pollen that they used to react to powerfully. But simultaneously, lots of seniors seem to lose tolerance to foods like shellfish, even if they’d previously been able to eat crab every single day.

Or maybe we just have no idea!

And finally, let’s give one last big shrug for all the other factors that seem to influence allergies that we don’t understand at all. A significant chunk of our most pressing allergy questions are simply unknown. Luckily, allergy research is exploding right now, so hopefully, we’ll have answers to those irritating questions soon. In the meantime, if you’re suffering from allergies, get personalized help. Allergists can identify your particular issues and will suggest treatment options, all of which (if you can afford it) will help you manage your allergies better.