If you're in mid-life (or beyond) and wondering what happened to your once-robust brows and lashes, you're sadly not alone. Eyebrow and eyelash thinning happens for a variety of reasons, including: autoimmune and genetic conditions, nutritional deficiencies, as a side effect to certain drugs or just good old-fashioned over-plucking (thanks, the '90s). However, among the more common causes for sparse brows and lashes is the hormonal changes that occur during menopause -- specifically, a decrease in estrogen. In fact, by age 50, at least 40% of women experience visible hair loss, including shedding some of the hair around and above our eyes. Scant "ghost" brows and lashes are yet another unpleasant part of aging no one tells you about until you're there. But, lucky for us follicularly-challenged folks of all ages, there are solutions to this beauty woe: both the best lash growth serums and the best brow growth serums can help.

According to board-certified dermatologist Dr. Ava Shamban, "yes," these products work -- but there are two different types and they function in different ways with varying efficacy and, maybe most importantly, disparate side effects.

"Natural" lash or brow growth serums, which are made with high-quality skin care ingredients and nutrients like vitamin E, won't generate new hair per se, but instead, "create a better environment for healthy hair to grow on its own," Shamban says.

"The ingredients in these [natural] growth serums eliminate dehydration, damage and breakage," she explains."They're designed to make your lashes and brows look and feel better because they are hydrated and coated to seal in moisture -- with a plumping effect so they appear thicker and more lush."

To that end, the best natural growth serums contain amino acids combined with emollients that benefit the skin, strengthen existing strands and keep the follicles clean and clear, all of which, "will promote the growth cycle of the existing hair so brows and lashes will appear more vibrant and dense," says Shamban.

The second category -- "chemical" lash and brow serums (like the popular Latisse) -- are more powerful, and are clinically proven to turbo-charge hair growth. They're made with a class of hypotensive drugs known as prostaglandin analogue, which are commonly used to treat glaucoma and, as a pleasant side effect, sprout new lashes in glaucoma patients.

"They help grow lashes [and brows] by keeping the growth phase longer so we see more, longer and better quality hair on our brows and lash line for longer periods of time," clarifies Shamban. Chemical growth serums yield darker, thicker, longer strands in many users -- more like the hair you have when you're young.

These products reap quality hair-growth results, but they can also introduce unpleasant side effects for some, particularly when used on lashes, and can even harm eyes or eyelid tissue. "[Chemical lash growth serums] can add a potential problem -- atrophy of fat in the superior sulcus and cause a hollow or 'deepening' around the eye," Shamban says. Other reported side effects of lash growth serums include redness, itchiness, and excessive watering, typically due to the chemicals involved.

Given these risks, while chemical lash growth serums may bring desired results, it's a good idea to consult with your healthcare provider before trying them -- particularly if you've had eye sensitivity in the past.

I asked Shamban for recommendations for quality brow and lash growth serums -- both natural and chemical. Some of her picks are those I've tested myself. Pro tip: While effective chemical products can be pricey, keep in mind, particularly with lash serums, this is not an item where you want to skimp on quality and, therefore, price.

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