Picking out the right sunscreen for your face is not only important for preventing sunburns, it is also one of your most powerful tools against sun-induced aging. Wearing sunscreen everyday is one of the most effective anti-aging measures in your skin care regimen, therefore it is imperative that you pick out the right sunscreen, and apply it properly.
Step 1: Know your SPF needs
If you are indoors all day and are exposed to the sun for fewer than 30 minutes every day then an SPF of 15 is adequate.
If you are exposed to the sun for more than 30 minutes a day (which is most people) use between an SPF of 30-50.
If you are unsure of how easily you burn, and how much SPF you need to protect yourself, check out the Fitzpatrick Classification of Skin Phototypes:
*Note the Fitzpatrick Classification recommends that you can go as low as an SPF of 4. However, because I am coming from both a scientific and skin care prospective, I recommend, regardless of ones ability (or inability) to burn, to stick to an SPF of 30 for long days out in the sun.
It isn't necessary to go higher than an SPF of 50 because studies have shown that the amount of protection that you receive after an SPF of 50 is minimal. You receive less than 2% of additional sun protection when using an SPF of 100 as compared to using an SPF of 50. Also note that SPF is primarily a measure of how well UVB rays are blocked.
Step 2: Choose a Sunscreen with Broad Spectrum Coverage
SPF is primarily a measure of how well you are protected against UV-B rays, the sun rays that cause you to burn. However, UV-A rays are just as important to guard yourself against because UV-A rays are the rays that cause photoagaing: sun spots, wrinkles, and loss of collagen and elastin. Therefore be sure to pick out a sunscreen that explicitly states on the package that it has broad spectrum coverage and protects against UV-A and UV-B rays.
Look at the Active and Inactive Ingredients
Active ingredients in sunscreen include all of the minerals or chemicals that give the sunscreen its SPF. If you prefer natural sunscreen, go with a mineral sunscreen containing zinc oxide and/or titanium dioxide. If you prefer a chemical sunscreen, check out this list of FDA-approved sun-protective chemicals.
Inactive ingredients include thickeners, emulsifiers (to mix oil and water), solvents (to dissolve ingredients), delivery agents (to deliver ingredients into skin), oils, extracts, alcohols, and preservatives. Know what works with your skin and what doesn't. My post here goes into detail about what oils are right and wrong for your skin type. Make sure that none of the inactive ingredients will irritate or inflame your skin, cause dryness, or cause acne or breakouts. Sunscreen is something you need to wear every day so make sure that the sunscreen that you are picking out is something you want to wear every day.
The FDA treats sunscreen like medication, and so you need to treat it like its medicine by applying the right "dosage." For the face, the dosage for sunscreen is 1/4 teaspoon. If you put less than 1/4 of a tsp on your face then you will get less SPF than what is advertised. You also need another 1/4 of a tsp on your neck and décolleté.
Since you need at least 1/4 tsp just on the face of pure sunscreen, this means that you should not rely on the sunscreen in your foundation because the SPF is diluted by the foundation.
Sunscreen should be the last step in your skin care regimen, and should be applied under the makeup. You do not need to wait to go outside after applying sunscreen because it works right away, however if you plan on going in the water it is best to let the sunscreen sit on the skin for least 15 minutes before getting wet. Also be sure to reapply after 80 minutes if you get your skin wet after applying sunscreen.