An attorney was asked to explain when someone can claim a medical exemption and whether a business can ask for proof of the medical exemption. You can read a copy of the attorney’s response. In short, upon asserting a medical exemption to wearing a mask, a business cannot ask for proof of the medical exemption. If you want to complete a self-assessment to determine if you have a medical exemption to wearing a mask, here are self-assessment forms for residents in New York, California, and Texas.