Many people with sensitivities react to carbon. I've had to return a couple of air purifiers because I reacted to the carbon. There are several types of carbon. Some companies sell a carbon testing kit that you can get before you purchase an air filter from them. It has several bottles with different kinds of carbon that you can expose yourself to by smelling it, keeping it open by your face during the night or however you choose to do it or muscle test yourself if you do that. I bought one at one time from a company who sells Allerair air purifiers. I reacted to every kind of carbon in there but one. When you do that, if I remember right you tell the company which type of carbon you want and they custom make your filter with that and I believe most of them then deduct the price of testing kit from the cost. It's been a while so I'm not sure I remember right. There is a company that sells Allerair purifiers. I can't remember the guy's name. I believe it was in Minnesota or some northern state. He was very knowledgeable and helpful.