[Niemand]

All the entries for allergies on p.78 say things like "while under the effects of the Allergy." or "while a character is under the effects of the Allergy."

How long do allergic reactions last? Is it different for environmental allergies versus substances?

If someone is attacked with a substance they're allergic to how long should the penalty last?

[Tecumseh]

It depends on the allergy.

For example, the Infected are allergic to sunlight. If they are no longer exposed to sunlight then the effects of the allergy cease. (Physical damage incurred by Severe and Deadly allergies remains until healed.) The same goes for other "contact" allergies, like seawater or precious metals.

If it is a dietary allergy, then the effects can persist anywhere from minutes to a week. The GM can decide on a case-by-case basis after factoring in dosage, severity of allergy, and any other factor they feel is pertinent.

[Kiirnodel]

Another way to think of it is "while still affected by the allergen."

For a lot of things it is probably going to be effectively while in an area where the allergen exists. But for many allergies it can potentially persist for some time afterward. For example

• I have an allergy to dust-mites, this effectively means that if something is really dusty or dust gets kicked up and it gets on my skin I get itchy and uncomfortable for awhile until I can get it off my skin. But it can also trigger an asthmatic reaction if I breathe it in (happened to me once when I was emptying a vacuum bag), I had trouble breathing for several hours because I couldn't just wash it off...
• I have a friend who is allergic to milk (not lactose intolerant, but actually allergic to something in milk products) if he isn't careful about what he eats, he ends up feeling ill for several days while it works its way through his system.