Summer myths, such as one shouldn’t swim for 30 minutes after eating, are bunk

Have you ever hesitated before diving into a pool, trying to remember if it’s been at least 30 minutes since you ate? Or not itched a mosquito bite for fear that scratching would only make it worse? Health myths buzz around summer pastimes such as swimming, camping, hiking and picnicking like so many gnats.

People have a hard time letting go of word-of-mouth wisdom, even when faced with good evidence to the contrary.

(Peter + Maria Hoey/TWP) - Poison Ivy is contagious but the rash itself is not.

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“Myths stick with us because they make sense to us, on some level,” says Indianapolis pediatrician Rachel C. Vreeman. “When you’ve heard them from your grandmother and mother and important adults in your life, you believe those things.”

Vreeman and fellow Indiana University School of Medicine pediatrician Aaron E. Carroll published studies in 2007 and 2008 debunking medical myths that doctors believe. Among them: Hair and nails continue to grow after a person has died. Shaving causes hair to grow back thicker. We use only 10 percent of our brains. Reading in dim light ruins your eyesight.

The studies received so much media attention that the doctors turned them into two books debunking many health myths: “Don’t Swallow Your Gum!” and “Don’t Cross Your Eyes . . . They’ll Get Stuck That Way!”

“It’s fair to ask ‘Why?’ when someone tells you you shouldn’t do something, even if that someone is your doctor or your mother,” Vreeman says.

Remembering the many warnings that swimming and outdoor activity inspire, we dug into some of the most pervasive summer health myths to find out whether they’re true.

Myth: Swallowing water-melon seeds is bad for you.

Swallowing a few watermelon seeds won’t do any harm, Washington nutritionist Rebecca Scritchfield says. Our bodies try to digest them but can’t, so the seeds pass directly through our system. Stay hydrated and continue to eat normally and everything will work out, so to speak. If someone were to chew up and eat every seed in a watermelon, the only danger would be overdoing fat and calories for the day, Scritchfield says. One cup of seeds contains 602 calories, 31 grams of protein (about the same as a chicken breast) and 51 grams of fat, a day’s worth for most people. Watermelon seeds are eaten in other parts of the world, such as Nigeria and China, Scritchfield says.

Small children might imagine that watermelon seeds could sprout in their stomachs (or be tricked into thinking this by a mischievous sibling). There have not been any reports of that happening — and it’s unlikely, given how strong digestive acids are — but in 2010, a pea seed did sprout in a man’s lung: A seed he had aspirated grew a half-inch-long sprout and had to be surgically removed at Cape Cod Hospital in Massachusetts.

Myth: You can catch poison ivy from someone who has it.

No matter how icky and oozy a poison ivy rash looks, the rash itself is not contagious, Vreeman says. It’s the oil from the poison ivy plant that is contagious, not the reaction to it that is the blistery rash you see on someone’s skin. “Leaves of three, let them be,” as they say.

Poison ivy causes a delayed response; the rash doesn’t appear for 24 to 72 hours after contact with the plant oils, which are found on the leaves and on the stems, and it can spread for days even without additional contact with the oil depending on individual reactions and sensitivities, according to the American Academy of Dermatology. By the time the rash is in full force, it’s unlikely the person would still have the oil on his or her skin. Washing the exposed area with soap and water for five minutes at the time of exposure may prevent the rash, says Ali Hendi, a Chevy Chase-based dermatologist.