A dermatologist weighs in with the proper MO.

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Sunscreen Bottles
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Quickly slap on some face sunscreen and dash out the door? For many, this familiar routine is the daily norm. Kudos for wearing SPF, but it's important to ensure you're applying it properly before you skip out for the day.

Dr. Elizabeth Bahar Houshmand, MD, a double board-certified dermatologist certainly knows a thing or two about sunscreen. The Texas-based doctor specializes in general dermatology, acne, and skin cancer. She walked us through how to apply sunscreen to your face, step-by-step. Read on, and soak all her savvy advice up.

WATCH: A Dermatologist Warns Against Using This Type of Sunscreen

"Broad-spectrum sunscreen should be the last step in your skin care routine before moving onto makeup. Use a tablespoon of sunscreen (of at least an SPF 30) on your face," says Dr. Houshmand, who recommends CeraVe Face lotion SPF 30. "Unless you slather on a thick layer, you're probably just getting an SPF 10 out of your SPF 30. Gently dot sunscreen onto your face. This technique helps it absorb more quickly and evenly. Make sure to apply a generous amount of sunscreen to your face after your moisturizer has dried," explains Dr. Houshmand. After you apply your sunscreen, wait at least 15 minutes before heading outside or putting on makeup so the sunscreen can absorb properly into your skin.

In addition to following this method for applying sunscreen to your face, she also advises that you use about a shot's glass worth (it's the equivalent of an ounce or so) from head-to-toe, such as Bare Republic Mineral Sport Lotion SPF 50. Reapply it every two hours or right after swimming or vigorous activity like jogging or playing a game of tennis.

It's also important you don't make these common sunscreen mistakes.Here are three of Dr. Houshmand's top offenders:

Only using sunscreen sometimes.

No excuses. You should be wearing sunscreen daily, even on cloudy days. "The majority of sun exposure is during your daily activities, meaning you get it driving in your car to get lunch or through your office window. You don't have to be at the beach or pool," notes Dr. Houshmand.

Using expired sunscreen.

This is a big no-no and frequent cause of sunburn. "Most sunscreens have a shelf-life between two and three years, however due to its unstable nature, bottles open for longer than one year should be thrown out. Additionally, if the expiration date has been reached, or if the sunscreen was left outside [of] room temperature, it's less likely to protect you," says Dr. Houshmand. Basket of suncreens from yesteryear roasting on the porch, we're looking at you.

Mixing sunscreen with other products.

Steer clear, everyone: "Mixing your sunscreen with lotions, creams, or other skincare products can dilute the active ingredients and reduce the SPF below what the labeling reflects," comments Dr. Houshmand. Yikes!