After getting an extreme allergic reaction (see here and here) from a day cream I randomly put on my face to prevent it from getting dry in the cold weather, I have been super very careful to say the least. It looked like eczema and felt like burn marks. My skin has always been really easy, it can handle just about anything, but I am never ever smudging any randomness on it ever again.
Now it is probably just one ingredient that I am allergic to and I do not know which one it is (those tests to learn which ingredients one can handle and which not are horrible!), but I will stick to the stuff that I have used before. Never again! Current favorites are these.