1. Sun Glare: You've barely settled onto your beach blanket when you gaze out at the dunes and a piercing pain rattles your skull. What gives? Glare. As light waves reflect off flat surfaces such as water, sand, and pavement, they intensify by syncing up, traveling in a horizontal plane of motion like a snake.
This can jog the brain's thalamus, a hub where pain signals are processed. Standard sunglasses screen out some glare, but the better bet is to slip on shades with polarized lenses, which contain vertical filters that block horizontal wavelengths, says John C. Hagan III, M.D., a spokesperson for the American Academy of Ophthalmology. Just be sure to choose a pair with 100 percent UVA and UVB protection.
2. Thunderstorms: No need to check the weather report—some people can predict a summer squall just by the throbbing in their temples. Blame the plunge in barometric pressure that precedes such storms.
This drop seems to rouse a sensory region in the brain that interprets stimulation as pain, says Merle Diamond, M.D., president of Diamond Headache Clinic in Chicago. Next time the weather turns iffy, she suggests trying a gentle form of exercise, such as yoga. Physical activity stimulates the release of endorphins, the body's natural painkillers.
3. Jet Lag: Traveling to a different time zone can leave you exhausted at noon or wired in the wee hours. That's a bother unto itself, but body-clock confusion can also spur the release of headache inducing inflammatory peptides, Diamond says.
To ward off jet lag, she advises nudging your schedule 30 minutes closer to your destination's time zone every day during the week leading up to your trip—for example, by waking up a bit earlier. Too late for the gradual approach? Skip the airplane snacks, then dine after you arrive. Research suggests that eating your first meal in accordance with local time can help the body adjust more quickly.
4. Heat: Several years ago, researchers at Harvard University analyzed hospital records and discovered that visits for severe headaches jumped by 7.5 percent for every 9°F increase in outdoor temperature. One possible explanation is that heat redirects blood to the head's peripheral tissues, a circulatory hiccup that may precipitate pain, says study author Kenneth Mukamal, M.D.
To determine your headache threshold, he suggests jotting down the day's temperature whenever you feel discomfort coming on. The pattern that emerges can help you be proactive—for example, by choosing indoor activities when the mercury creeps past 88°F.
5. Dehydration: You already know the hot sun can dry you out, but a parched mouth isn't the only sign of dehydration. Fluid loss also sensitizes pain receptors in the thin layers of tissue that encase the brain, says Alexander Mauskop, M.D., director of the New York Headache Center and coauthor of What Your Doctor May Not Tell You About Migraines (Grand Central Publishing).
The risk of a headache is even higher when you swim because water activities forestall feelings of thirst. Whenever you're outdoors for extended periods, aim to sip 8–12 ounces of water or another nonalcoholic beverage every 1 to 2 hours, even if you don't feel particularly dehydrated.
6. Hot Dogs: Most franks—as well as other cured and processed meats such as bacon and cold cuts—contain sodium nitrate or sodium nitrite, two chemical preservatives that enhance color and prevent bacterial growth.
For some people, these additives can bring on headaches by overdilating blood vessels in the head, putting the squeeze on nearby nerves, says neurologist David Buchholz, M.D., author of Heal Your Headache (Workman Publishing). If you think you might be affected, stick with fresh whole cuts of meat, such as steak and chicken drumsticks, at your next cookout; they're generally preservative-free.