Here is how it happens:

You get a new pair of shoes. You take them out of the box and put them on. They are black sneakers in leather and suede, and you love them. They feel good on your feet, and they look good, too.

Two hours in, you feel the headache coming on. It’s that same old headache—the one that starts behind the eyes and then seems to inflame your brain so that it squeezes against the insides of your skull, and because you have multiple chemical sensitivity, you look around and wonder why. What has changed in the air? Nothing, it seems.

And then you look down and you remember your shoes. Your new shoes. You lift one foot up to your nose and take a whiff. You recoil at the sharp, acrid odor. You don’t know what it is, but you know it is a chemical and that the way out of this headache is to remove the shoes. You are not happy to take them off, but you do. You put them in the next room and close the door. You crack the window even though it is winter and bitter cold outside. The headache fades and you forget about it. But it is not far away.

Later, you tear the plastic wrapping off your new calendar and start paging through, admiring the photographs of dark clouds and powerful storms. Suddenly you ask yourself, Why am I getting the headache again? You can’t imagine the reason. You keep flipping through the calendar, and then, when you get to the month of May, you catch the scent. A potent chemical odor. But you want to see the photographs. You flip through faster. Then you hurry out of the room, new calendar in hand, and take it to the furthest reaches of the house. The headache is back, full on. You try to read but all you can think to do is regret that you didn’t run the calendar out of the room the instant you noticed that it was toxic.

This is your life, and you’re so used to it you barely think to make note of it. But then you do. You want others to know.

Maybe this headache will be gone in the morning. Probably it will.