—Bonnie Baer, Centre Hall, Pennsylvania According to the National Institutes of Health, a stunning 35 percent of people have adverse reactions to scented products. The scents may be allergens or irritants that cause responses ranging from migraines to wheezing to nausea. But why? Scents are composed of a vast array of chemicals whose only reason for their particular combined existence is to mask unpleasant odors and/or create a pleasing smell. This means we’re inhaling substances intended to affect human olfactory neural circuits. That’s invasive, so it’s no wonder that it goes wrong so often.