Yes. Our bodies change over the years, and we can build up tolerance or become intolerant to certain things that we never before. To work out what it would be that's causing problems best thing to do is eliminate things and see if you start seeing a difference.
Normally, during the course of evolution from a baby to an adult, we develop a mechanism by which we desensitize ourselves to all the materials we are exposed to. But sometimes, the desensitization may not be perfect and we develop allergic reactions to those few substances. On exposure to the allergen, an Immunologic (IgE) or a non-immunologic reaction is set in process, which ultimately releases histamine, which acts at the peripheral receptors, resulting in allergic reactions. So, we can develop allergic reactions at anytime.
It may help to maintain a food dairy and keep monitoring your symptoms. This will help to narrow the search and avoid them.
Most definately food allergies can come and go. It is very common actually for example for children with lactose intolerance allergies to actually get better ;and also vice versa for kids who weren't and then when they get into adulthood they become allergic to it. If you eat too much of one thing all the time your body can become intolerant of it and can cause an allergy. And finally yes, it is very possible to have a food allergy and not realize it until you have a reaction. If you fear you have an allergy to a food the best thing to do is get it tested at the doctors office and until doing so avoid consuming that product. Good luck to you!
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