It is believed that we have more allergy issues then previous civilizations because of our high level of sanitation. The evidence is that early exposure to dirt and close proximity to animals prime our immune systems for appropriate response. Because we live so much more cleanly today and rarely live in close proximity to a range of animals our immune systems over-react to allergins.

For example, it recently was found that, "early-life microbe exposure decreases the number of inflammatory immune cells in the lungs and colon, lowering susceptibility to asthma and inflammatory bowel diseases later in life." (http://www.the-scientist.com/?articles.view/articleNo/31879/title/Let-Them-Eat-Dirt/)

Speaking from an ancient Greek view and as a father to a daughter with several food allergies. I have tried in vain to find anything in early sources that even sounds like an allergy. They were just completely unknown. So it seems to me that it is practically impossible to determine how common or uncommon allergies were. It is simply an exercise in logic, without source material to back anything up.

There are several theories as to why allergies are more common now then in earlier times, but I've never seen anything that proved to me that allergies are definitely more common now and not that, for instance, we are just better at diagnostics due to blood and skin testing. We might simply test more because doctors and parents are more aware of it. It is really hard to say, IMO.

Take an allergy to milk. An ancient person might have thrown up when they drank certain milk. But they might not have regarded it as any particular disease, but simply avoided milk because it didn't agree with them.

If anyone has any ancient evidence of allergies, though. I would love to hear about it.

Related but also very different.. Was bad vision as widespread as today? Did they try ways to correct that or would they even have really known?