The Short Answer

Latisse works by making your eyelash growth phase last longer. The active ingredient — Bimatoprost — signals your eyelash hair follicles to keep growing instead of stopping and shedding. The result: lashes that are measurably longer, thicker, and darker.

But there's a lot more to the story. Let's break down the science in plain English.

First, How Do Eyelashes Normally Grow?

Your eyelashes don't just grow continuously. Like all hair on your body, each individual lash goes through a repeating cycle with three main phases:

1. Anagen Phase (Active Growth)

This is when the lash is actively growing from the hair follicle. For eyelashes, this phase typically lasts about 30 to 45 days. During anagen, the follicle is producing new cells, and the lash gets progressively longer.

2. Catagen Phase (Transition)

After the growth phase ends, the lash enters a transition period lasting about 2 to 3 weeks. The follicle shrinks and the lash stops growing, but it stays in place.

3. Telogen Phase (Resting and Shedding)

The final phase lasts about 3 to 4 months. The old lash rests in the follicle while a new lash begins forming underneath. Eventually, the old lash falls out and the new one takes its place, starting the cycle over.

At any given time, your lashes are at different stages of this cycle — which is why you don't lose them all at once. Most of your lashes (about 80–90%) are in the anagen or telogen phase.

What Bimatoprost Does to the Cycle

Bimatoprost, the active ingredient in Latisse, primarily affects the anagen (growth) phase in two key ways:

It Makes Anagen Last Longer

The biggest effect is that Bimatoprost extends the anagen phase. Instead of your lash growing for 30–45 days and then stopping, it might grow for 60 days or more. Since the lash is growing for a longer period, it reaches a greater length before entering the transition phase.

This is the main reason Latisse makes lashes longer — they simply have more time to grow.

It Stimulates More Follicles Into Anagen

Bimatoprost also appears to increase the percentage of hair follicles that are in the active growth phase at any given time. This means more of your lashes are actively growing simultaneously, which creates the appearance of thicker, fuller lashes.

It May Increase Melanin Production

Clinical trials showed that Latisse makes lashes darker. This is believed to be due to increased melanin (pigment) production in the hair follicle during the extended growth phase. The longer the follicle is active, the more pigment it deposits into the lash.

The Molecular Science (Simplified)

For those who want a bit more detail on what's happening at the cellular level:

Bimatoprost is classified as a synthetic prostamide analog. Prostamides are substances related to prostaglandins — signaling molecules that your body produces naturally. Prostaglandins play roles in inflammation, blood pressure, and many other body functions. They also influence hair growth.

Bimatoprost mimics the action of natural prostamides and binds to prostamide receptors on cells in and around the hair follicle. When these receptors are activated, they trigger a cascade of cellular signals that:

• Prolong the growth phase of the hair cycle
• Stimulate the dermal papilla cells at the base of the follicle (the cells responsible for driving hair growth)
• Increase blood flow to the follicle, providing more nutrients
• Enhance melanogenesis (pigment production)

Scientists are still working out all the details. The exact receptor pathway isn't fully understood — Bimatoprost doesn't perfectly fit the known prostaglandin receptor categories, which is why it's classified as a "prostamide" rather than a traditional prostaglandin. This is an active area of research.

How Is This Different from Glaucoma Treatment?

Here's an interesting bit of Latisse history. Bimatoprost was originally developed and FDA-approved as a glaucoma medication under the brand name Lumigan. When used as eye drops for glaucoma, Bimatoprost lowers intraocular pressure (IOP) by increasing the outflow of aqueous humor (fluid) from the eye.

Doctors noticed that their glaucoma patients were developing remarkably long, thick eyelashes as a side effect. AbbVie (then Allergan) recognized the potential and developed a lower-concentration topical formulation specifically for lash growth — that became Latisse.

Key differences between the two products:

• Lumigan (glaucoma): 0.01% or 0.03% Bimatoprost, applied as an eye drop directly into the eye
• Latisse (lash growth): 0.03% Bimatoprost, applied topically to the skin of the upper eyelid margin with an applicator — not dropped into the eye

Because Latisse is applied to the skin and not into the eye, much less Bimatoprost actually enters the eye compared to Lumigan. This is why certain side effects (like iris color change and significant IOP changes) are much rarer with Latisse than with Lumigan.

Why Does It Take 16 Weeks for Full Results?

Understanding the hair cycle explains why Latisse requires patience. Here's the timeline:

• Weeks 1–4: Bimatoprost is beginning to affect your follicles at the cellular level, but your current lashes are still in whatever phase they were in when you started. You probably won't see any visible change yet.
• Weeks 4–8: Lashes that were in early anagen when you started have now been growing for longer than they normally would. Some initial lengthening may become noticeable.
• Weeks 8–12: More lashes have cycled through and entered an extended anagen phase. You'll notice more obvious improvements in length and fullness.
• Weeks 12–16: By now, most of your lashes have gone through at least one full cycle under the influence of Bimatoprost. This is when you see maximum results.

In clinical studies, Latisse produced an average 25% increase in lash length, 106% increase in thickness (fullness), and 18% increase in darkness after 16 weeks of daily use.

Why Do Lashes Go Back to Normal If You Stop?

Latisse doesn't permanently change your hair follicles. It influences the growth cycle only while you're using it. Once you stop applying Bimatoprost, your follicles return to their normal programming — the anagen phase goes back to its original length, fewer follicles are in the growth phase simultaneously, and your lashes gradually return to their pre-treatment appearance.

This typically happens over several weeks to months after discontinuation. It's similar to how your hair would go back to its natural state if you stopped using a growth-promoting treatment.

Does Latisse Work for Everyone?

Latisse works for most people, but results vary. In clinical trials, the vast majority of participants saw measurable improvements. However, some factors can influence your results:

• Starting point: If you already have moderately full lashes, the improvement may be less dramatic than for someone starting with very sparse lashes.
• Consistency: Skipping doses reduces effectiveness. Nightly application is important.
• Genetics: Individual hair growth biology varies, and some people may respond more or less than average.
• Other conditions: Underlying medical conditions affecting hair growth (like thyroid disorders) may influence results.

If you're interested in trying Latisse, learn how to find a prescribing doctor near you. For a complete overview of the medication, see our guide on what Latisse is and how to use it.

Concerned about side effects? Our detailed breakdown of Latisse side effects covers everything you need to know. And if cost is on your mind, check out how to save money on Latisse.