If you haven't been using makeup primer, then you're really missing out. Whether you wear a full face of makeup everyday or you prefer to keep it simple with BB cream and tinted lip balm, makeup primer is a godsend when trying to combat shine or create a smooth base for foundation.

Yet, many people often skip this step because they believe they don't really need it, are unsure of how to use it or don't think it's worth the investment. However, using primer underneath your makeup will make everything last longer, whether that's on your skin or in your cosmetics bag. We asked two beauty experts to discuss the ins and outs of primer and why it's a must-have. Here's the deal.

Makeup primer is a base for foundation or face makeup that allows it to go on smoother and last longer.

Formulas are available in cream, gel and powder. While moisturizer softens skin, editorial and celebrity makeup artist Stephen Dimmick points out that primer prepares skin for your favorite tinted moisturizer or foundation, giving it something to hold onto so it lasts throughout the day.

Many makeup primers are formulated with silicone-based polymers like dimethicone because of their ultra-smoothing effects. But for those who struggle with cystic acne and other skin conditions, do a patch test or check with a medical professional before use, as there have been reports of allergic reactions to dimethicone.

Physicians Formula's celebrity makeup artist Joanna Schlip adds that makeup primers can also help smooth any fine lines, wrinkles or large pores. If you are searching for a face primer to help color-correct rosacea or conceal acne spots, Schlip's go-to is this light green primer as that hue cancels out redness.

Primers are even available just for your eyelids to prevent creasing. "I'd recommend pairing a primer with extra long-wear [eyeshadow or eyeliner] formulas for a look that will really stay put," says Schlip. If you have oilier eyelids, Dimmick advises that you use a mattifying eyelid primer. Using your fingertips to apply makeup primer allows you to really work the product into your skin.

Schlip thinks it's best to apply primer with fingertips for areas larger than a quarter. "If only using for small areas, I'd recommend a brush. I like to use a concealer or lip brush for this," she said. This spot-treat technique gives the look of a more natural finish, according to Schlip.

Taking this routine a step further, Dimmick considers the process "an exercise for the face." He explains that massaging primer onto skin with fingertips helps "to get the blood flowing underneath." We'll consider that the next time we're meditating while putting on makeup. Primer for makeup is a life-saver for getting your makeup to stay-put in extreme weather.

If you live, visit or plan on traveling anywhere that experiences hot and humid or cold and dry temperatures, Schlip suggests having primer handy to help your makeup wear longer. However, Dimmick advocates for using primer year-round. "No matter what the weather is like outside, this extra step will save you a lot of time and effort."

Primer can even be worn on its own. Love the fresh no-makeup look but want to look a bit more polished than when you first woke up? Primer is your answer. The product can be worn on your eyelids and double as a light eyeshadow, or it can serve as a lighter alternative to foundation.