Dr. Dutta tested me for environmental allergens. This is one of my favorite medical experiences. They dot your arm with magic marker and prick your skin in rows on each side to keep track. When they see a reaction (a raised bump with redness) they repeat that allergen on your shoulder. I reacted to dog and cat, dust mites, and Ash tree pollen.
I didn't care too much about the Ash trees, but there is a four-legged allergen in my house named, Chicken. After too much contact, I sneeze twice and my nose plugs up. There's no chance of getting rid of her. She spends a lot of time in our bed, so when I lie down I often get stuffed up. My nose isn't very functional, but being stopped up is unpleasant and may contribute to my snoring.