When you have short eyelashes, the allure of having long lashes is omnipresent. I'm constantly fantasizing about a world in which I have long and fluffy fringe sans mascara. So naturally, the prospect of a lash serum is enticing, but do lash serums work? The good news is: Yes, lash serums can work—but it's not always simple, straightforward, or guaranteed.

"The effectiveness of lash serums can vary from person to person and from brand to brand," says board-certified dermatologist Bertha Baum, DO. "Some people may experience noticeable lash length and thickness improvements after using them consistently. In contrast, others may see little or no results. It's essential to manage expectations, as results may take several weeks to months to become apparent."

Learn what makes a lash serum good, how prescription offers differ from over-the-counter options, and more, below.

Meet the expert

What Makes Lash Serums Effective

"Lash serums are eyelash treatments that promise healthier, fuller lashes by using a variety of ingredients to nourish and boost lash thickness and growth," says board-certified ophthalmologist Diane Hilal-Campo, MD. "They are generally applied along the upper lash line or through the length of the lashes."

Dr. Hiilal-Campo, who is also the founder of eye-friendly beauty brand twenty/twenty beauty explains that these serums include ingredients that strengthen, moisturize, and nourish the lashes.

As she puts it, "Helpful ingredients include castor oil, which hydrates the lashes and increases the blood flow to the lash bases, taking them from resting to growth phase; argan oil, which is rich in linoleic acid that coats, moisturizes and thickens lashes; peptides, which are believed to stimulate hair growth at the follicles; keratin, which is a natural protein found in hair that strengthens it; sodium hyaluronate, which acts as a humectant locking in moisture; and biotin, panthenol, and other vitamins that supplement hair growth."

Prescription Lash Serums vs. Over-the-Counter Options

"Prescription lash serums, such as Latisse, differ from over-the-counter (OTC) options because they contain active pharmaceutical-grade ingredients," says Dr. Baum. "Latisse, for example, is approved by the Food and Drug Administration (FDA) and has been shown to increase lash length and thickness effectively. However, they may also have a higher risk of side effects, such as red or irritated eyes, which I highly recommend discussing with your dermatologist."

Dr. Baum also notes that in rare cases, Latisse (generic name bimatoprost) has been linked to skin discoloration and a change in the color of the iris when used in patients with lighter eyes. However, this latter side effect is really only a concern when bimatoprost is put in the eye, not around it. "It's a side effect that was discovered during clinical trials for bimatoprost eye drops that are prescribed to glaucoma patients. And only about 1 percent of people in the trial for the glaucoma eye drops experienced eye color change," explains Dr. Baum.

Dr. Hilal-Campo adds that bimatoprost and its cousins (PGF2 alpha analogs, which can be sold OTC) can also contribute to periorbital fat atrophy, causing sunken eyes and a deepening of the upper eyelid hollow; plus, chronic dry eyes from damage to the meibomian glands.

Because the ingredients in OTC lash serums aren't as potent as those in prescription formulas, they may also be less effective, explains certified physician assistant Nevada Norris, PA. "Over-the-counter lash serums often contain less potent ingredients and still provide some benefits for lash health and appearance, but are usually less powerful than prescription serums," says Norris.

How to Get the Most Out of Your Lash Serum

Whether you get a prescription or OTC option, Dr. Hilal-Campo recommends performing a patch test. "Any lash serum can cause an allergic reaction, so you really should patch test the serum for 24 to 48 hours on the inner arm before using," says Dr. Hilal-Campo.

If your patch test goes well, you can start applying it, keeping in mind that consistency is key. Most lash serums will instruct you to apply the serum daily, but follow the instructions on your package closely. "It's also important to note that once you stop using the serums, the increased lash hair growth that resulted from using the serums will cease, as well," says Dr. Baum.

Lash Serums the Pros Love

Both Dr. Baum and Norris swear by Latisse and constantly recommend it to their patients . "It has proven to be the most effective among my patients and myself," says Norris. Dr. Baum adds: "Usually, results may appear within four weeks, but full results take sixteen weeks."

If you prefer an OTC option, Dr. Baum recommends Neutrogena Healthy Lash and Brow ($14) and Norris recommends Alphalash ($132). Envious Lashes founder Clementina Richardson recommends the Lash Conditioning Serum ($59) from her line. And Dr. Hilal-Campo recommends The Ordinary Multipeptide Lash Serum ($15), Vegamour GRO Lash ($72), and, of course, the Get Growing Lash and Brow Serum ($52) from her line. "My Get Growing Serum does not contain any analogs of PGF2 alpha, and it does not need or have a preservative in it, which can be irritating and exacerbate dry eyes," says Dr. Hilal-Campo. "It is actually soothing and hydrates the lashes, lids, and eyes."