As I shared in Part I, getting some sun is good for you, at least if you’re smart and careful about it.

Your first step to that end: get some good sunscreen.

Sunlight is made up of two kinds of ultraviolet rays: UVA and UVB. It’s the latter, UVB, that causes sunburns, so for decades sunscreen was designed to block UVB. But more recently, research has shown that UVA rays, which penetrate deeper, also substantially increase skin cancer risk, and cause wrinkles. (The EPA estimates that up to 90% of aging-related skin changes are actually caused by a lifetime’s exposure to UVA.)

Good sunscreen is therefore ‘full spectrum’ or ‘broad spectrum’, and blocks both UVA and UVB. While those were previously specialty products, in the last year or two, almost all the major sunscreen brands have released reasonably-priced, widely-available versions that block both spectrums. Make sure you only buy sunscreens that do.

Three more sunscreen tips: slather it on, do it often, and stop going nuts with the SPF.

According to the American Academy of Dermatology, most people apply only 25-50% of the amount of sunscreen that they need per application, which reduces an SPF 30 sunscreen to an SPF 3. SPF ratings are based on applying two milligrams of sunscreen per square centimeter of skin. Which is a lot. Basically, you should briefly look like Casper each time you apply a layer if you want your sunscreen to actually do anything.

Next, a sunscreen is FDA-certified as ‘water resistant’ if it can hold up to 40 minutes of swimming or sweating. After that, all bets are off. So, while you’re on the beach, you also probably need to reapply every hour or so.

And, finally, just buy some SPF 30; after that, the numbers get kind of meaningless. A few years back, Procter & Gamble even sent a letter to the FDA, asking that the numbers be capped at 30, because real-world and laboratory light conditions are different enough to make higher SPFs of “dubious value” that are “at best, misleading to consumers.”

So, to recap, buy some SPF30 full-spectrum, water-resistant sunscreen. Put on a bunch, and keep reapplying. And then enjoy the sun!