MCS occurs as the body reacts to a chemical or family of chemicals.
Many persons are at least very mildy sensitive to thousands of chemicals.
For some persons, though, their body reacts very strongly to several chemicals. Refrain from wearing strong colognes, perfumes, and strong fragrances. Wash your clothing in unscented detergents. Avoid spraying air freshners. Wear no colognes, perfumes, fragrances, after-shaves, etc.