"There are certain ingredients that actually provide effective protection against UVA. The three most common include zinc oxide, titanium dioxide and something called Avobenzone, or parsol 1789," Herschenfeld said.
She recommends using products with the first two ingredients, especially for children.
But be careful if you're relying on Avobenzone. It degrades quickly in the sun, so keep putting it on, or look for a stabilizer like Helioplex, available now in just two products approved for sale in the United States: Neutrogena with Helioplex and Aveeno Continuous Protection Sunscreen. Outside the United States, look for products with the ingredient Mexoryl.
Too much science? Well, this part's easy.
Stay in the shade during peak sun hours. When you do venture out, apply sunscreen early -- at least 20 minutes before you go outside. Be generous with it: use about four times what you think you need, and reapply it all day long , especially, if you go into the water.
"There is no way to produce a sunscreen that is truly waterproof. The best it can be is water resistant," said Herschenfeld.
It may sound like a lot of work for a little sunshine in your life, but keep in mind, even with all the sunscreen, the incidence of skin cancer is on the rise. Melanomas, many sun-related, have doubled over the last 25 years.
But that doesn't mean you're condemned to stay inside.
"I don't tell my patients to be hermits. I tell them to put on their hats and their sunscreen and their sunglasses and get out there," Herschenfeld said.
You might think it's just the sun that causes premature wrinkles and ages your body, but a growing body of research shows your own anxiety levels can take years off your life.
"Stress is the greatest ager of all and it's the only thing we know that causes an increase in arterial aging, heart disease, strokes, memory loss … immune aging, infections and cancer," said Roizen.
So how does stress attack your body? That's exactly what Ronald Glaser and his wife, Janice Kiecolt-Glaser, have been studying for 25 years. Their research actually began as a marital disagreement. Janice, a psychiatrist, believed stress harms the body; Ronald, a molecular virologist, did not.
"There were a lot of skeptics, and I was one of them," he admitted.
And what better subjects to test for stress than med students taking exams?
Early on in their research, the Glasers exposed their subject to microbes via a vaccination.
"We found immune changes associated with them taking the exams, and quite frankly, I was absolutely blown away with that," Ronald Glaser said.
More than two decades later, the couple is studying whether the stress of fighting with your spouse would slow the body's healing. The researchers created blisters on the volunteers' forearms and then stressed the couples by making them talk about their pet peeves. All the while, the researchers analyzed their blood and tissues samples.
"We found that even a minor stress can really slow how fast you heal," said Janice Kiecolt-Glaser. She also noted that when couples argued, they took longer to heal.
Surprisingly, not all types of stress actually damage the human body. Ironically, it's those nagging tasks that you put off that'll drive you nuts and age you.
"For one nagging unfinished task, it puts on about eight years on your life. So if you're 30, it makes you 38," said Roizen.