I am very allergic to cows' milk.
I wasn't always allergic. I used to eat all kinds of milk products just like any other typical American. In my late twenties, I started to notice that when I ate large amounts of milk (like a yogurt AND cereal with milk for breakfast), my stomach hurt and I would get gastrointestinal problems. Most people in the world are lactose intolerant, so I figured that this was my problem as well. However, taking lactaid didn't seem to help the problem; instead, I became more and more sensitive to milk. I also began developing other symptoms, like swelling, aching muscles, a stuffy nose, allergic shiners (dark circles around the eyes) and so on.
Apparently I have a milk allergy. My grandmother had one, which also developed in her late twenties, so perhaps it's genetic. In any case, it's a really tiresome thing to have. Whenever I ingest any milk, even a small amount, I become sick within a few hours. It feels like having the flu (aches, exhaustion, vomiting, diarrhea) and lasts 1-2 days. The severity of the reaction depends on how much milk I've had, but even a small amount (like from eating baked goods containing butter) is enough to make me miserable. The only thing that helps is vomiting as soon as possible after eating milk, and taking Benadryl (which I hate because it's so sedating).
It's a really troublesome allergy, especially in the US. Milk sneaks into thousands of products: most crackers, whole wheat bread, soups, prepared meat (like salami), desserts, margarine and highly processed foods are out of bounds, in addition to the obvious foods like sour cream, cheese, ice cream, butter, whipped cream, etc. Even red wine can contain casein (which is the part of milk I'm allergic to). Eating out is always really difficult, because so many restaurants make food taste good by cooking everything in butter. I try my very best to be careful, but it's not always possible, especially as most people don't seem to realize that butter and cheese are milk products (I always must ask separate questions about this).
Today I went to my sister's house and she served me a sandwich on homemade bread that her husband made. It contained butter, as we found out after I'd eaten half of it, and now I am puffy (my fingers swell up), gassy, have heartburn and feel nauseous (I took benadryl so hopefully this will be the end of it). Also I look awful as I always get really pale with huge dark circles under my eyes. Stupid milk allergy.