CNN —  

The thinking used to be that germs were bad and clean skin was good — adds up, right? But science has recently debunked that theory. If anything, many germs are good. In fact, our skin microbiome, the community of microorganisms that lives there, is made up of more than a trillion bacteria in and on our skin, comprising about 1,000 different species.

But these bacteria aren’t created equal.

“Your skin microbiome is in a constant balancing state between harmful and helpful microorganisms,” says Dr. Howard Sobel, a dermatologist in New York. Probiotics, beneficial bacteria that you can add to the mix, support the health and population of those helpful microorganisms, keeping the microbiome (and therefore your skin) in balance.

On the skin, they serve some essential functions. “Probiotics fight bad bacteria in our gut and on our skin, help regulate our immune system by working to control inflammation, and support the healthy barrier function in both our gut and skin,” says Dr. Whitney Bowe, a New York dermatologist and author of “The Beauty of Dirty Skin.”

But certain habits can decimate those delicate good bacteria, throwing your microbiome out of balance and allowing the bad bacteria to take over. “When we over-scrub and over-exfoliate our skin, we are compromising our skin’s barrier,” explains Bowe. “When our skin barrier is not intact, it is no longer preventing allergens and irritants from entering the skin and is unable to adequately trap moisture in the skin to keep our skin healthy and hydrated.”

That can open a Pandora’s box of sorts for skin, leaving it vulnerable to inflammatory skin disorders, such as psoriasis, eczema and acne. A dysfunctional microbiome can also increase premature aging and sensitivity, meaning your skin begins to burn or sting unpredictably when you use certain skin care products.

Reintroducing those good bacteria to skin can help restore your skin’s protective moisture barrier, minimize inflammation, and keep bad bacteria in check. “Look for antioxidant-rich formulas that use natural probiotics without any harsh allergens or irritants that could potentially compromise the health of your skin,” Sobel suggests.

Products that contain prebiotics, fiber that feeds probiotics, can also help. “Prebiotics are like the nourishing food that naturally allows good bacteria to thrive on your skin,” Bowe explains. “Some prebiotics encourage specific healthy strains of bacteria to grow, and others increase the diversity of the bacteria on your skin, which is also very important.”

Here, some of our favorite probiotic skin care products to try.

Biossance Squalane + Probiotic Gel Moisturizer ($52;

In this lightweight moisturizer, probiotics are paired with squalane, a deeply nourishing ingredient derived from olives.

Sweet Chef Ginger Kombucha + Vitamin D Chill Mist ($17;

A base of ginger kombucha, which is naturally rich in probiotics, gives this refreshing mist the power to nourish and balance skin in seconds.

Korres Hydra-Biome Probiotic Superdose Face Mask ($49;

Not only does this Greek yogurt-enhanced mask offer both probiotics and prebiotics, but it also delivers moisture to skin for up to 48 hours.

Algenist Alive Prebiotic Balancing Moisturizer SPF 15 ($27.83, originally $40;

Get your prebiotics, probiotics, hydration and sun protection in a single step with this multitasking formula.

StriVectin Multi-Action Blue Rescue Clay Renewal Mask ($48;

Ideal for acne-prone skin, this clay mask offers a one-two punch of pore-clearing power and skin-balancing bacteria.

Beautyblender Re-Dew Set & Refresh Spray ($30;

Keep your bacteria balanced throughout the day — and your makeup fresh — with this hydrating setting spray.

Unwash Balancing Scalp Serum ($22;

The scalp is often overlooked, but it can get just as irritated or off-balance as your face. (Hello, itchiness and sensitivity.) This prebiotic- and probiotic-packed scalp treatment brings it back to health.

La Roche-Posay Lipikar Balm AP+ Intense Repair Moisturizing Cream ($19.99;

If you’re partial to hot showers in the winter, slather this on afterward to keep your skin healthy and hydrated. Prebiotics support your skin’s good bacteria from head to toe, and this cream is so good at repairing the moisture barrier that it was accepted by the National Eczema Association.

Note: The prices above reflect the retailers’ listed prices at the time of publication.