UVA rays, which play a large role in causing the signs of premature aging, such as wrinkles, discoloration, and loss of firmness, can penetrate windows and clouds. Even if you can’t see the sun, a broad-spectrum sunscreen (which means it protects the skin from both UVA and UVB rays) will help shield your skin from these visible effects.

Without proper protection, UVB rays increase your risk of sunburns and skin cancer, while UVA rays expedite visible aging (think: fine lines, wrinkles, sagging, dullness and dark spots). UVA rays can penetrate through the skin’s deepest layers, including the dermis. This layer produces collagen and elastin, the proteins responsible for bouncy, firm, and taut skin. UVB is known to penetrate the epidermis, which is the uppermost level of skin.

When it’s impossible to completely avoid sun exposure (remember: you’re not protected from the sun on overcast days or when indoors with windows) using a broad-spectrum sunscreen is the next best tool you have to maintain youthful-looking skin for as long as possible. The ideal sunscreen will be broad-spectrum to protect against UVA and UVB rays and formulated with moisturizing ingredients that help to improve the appearance of dry, dehydrated skin.

Absolutely. But here’s the caveat: If you apply, say, a foundation with SPF, you might not be using enough of the product to achieve the intended level of protection. That’s because sunscreen effectiveness partly depends on how much you put on. For instance, half a teaspoon of sunscreen should be applied on your face and neck combined. Most people don’t apply that much foundation. To make sure you get the right amount, it’s best to layer on a standalone broad-spectrum sunscreen under makeup.

Physical sunscreens include zinc oxide and titanium dioxide. They stay on top of the surface of skin to physically shield and reflect UV rays. Chemical sunscreens, on the other hand, absorb UV rays and commonly include homosalate, octisalate and octocrylene. The ideal broad-spectrum sunscreen will include both types since physical filters don’t cover the entire UV spectrum.

Sunscreen ingredients, when expertly formulated in combination with each other, can provide broad spectrum UVA and UVB protection. In addition, antioxidants like vitamin C may help to defend against the effects of environmental stressors and mitigate signs of cumulative sun exposure such as dark spots and discoloration.