Stress is the main ingredient in MCS. Most people who have MCS do not handle stress well. There are several techniques for reducing or quieting stress - breathing, dropping into your heart with HeartMath, meditation, focus, yoga, relaxation, etc.
A key stressor can be not accepting reality. Sometimes those of us with MCS don’t want to accept that we are that sensitive to chemicals. Or at least we don’t want to believe that we are that sensitive to certain chemicals or fragrances. But just because we don’t want to believe it, that doesn’t mean that it’s not true. And fighting the truth can be very stressful.