We cannot say for certain. It is our understanding that people with MCS can react to a variety of chemicals and products. Not all products that they can react to are highly toxic (i.e. laundry detergent). MoldAvenger does have a light lemon fragrance to it. For a customer with MCS, the manufacturer recommends testing a small amount of product to see how they do with it. It is also recommended to have someone else mix the powder with water (the powder has a much stronger fragrance than the product does when diluted). MoldAvenger is known for being a less toxic solution for mold control. Hopefully the product will be compatible in most instances.