When it comes to getting a healthy dose of vitamin D, you can go from sun kissed to scorched quicker than you realize—and, according to the Center for Disease Control (CDC), if over exposed year after year, the long-term effects are damaging, increasing your risk of premature wrinkles, age spots, and skin cancer.

Sunburns usually show 4 hours after exposure. But with the application of sunscreen, keeping your skin safe from sunburn and other tanning related skin conditions is possible. So, what does that SPF mean in your sunscreen? The CDC explains that the SPF refers to the amount of time that a person can stay outside in the sun. So for example, SPF 15 allows someone to stay outside 15 times longer without burning.

In short, sunscreen works, said Kenneth Svensson, MD, of Highland Medical- Dr. Kenneth B. Svensson Family Practice. To reap the most benefits, it’s recommended to apply it 20 minutes prior to sun exposure and to reapply every two hours. Keep in mind that wind, perspiration, and water play impact the application, so if you feel like you should reapply sooner than 2 hours, do it.

Source: www.cdc.gov/niosh/outdoor-workers/about/sun-exposure.html