✅ Medically reviewed by Dr Tom Walker – 19/03/2026
If you are considering using the a lash growth serum it is entirely reasonable to ask “what are the potential side effects and how common are they?”
One of the most common treatments for lash growth is a solution of bimatoprost 0.03%. It is generally well tolerated when used correctly with side effects being rare, but like any medically active treatment it can cause side effects in some individuals.
Most patients who use the solution correctly experience no side effects.
Understanding these properly rather than relying on online anecdotes is key to making an informed decision.
What Is BIMATOPROST?
Bimatoprost is just one of the active ingredients offered by Mylash under consultation for lash growth. It is well known as an effective active ingredient, through its association with a US brand.
Bimatoprost is a prostaglandin analogue originally developed to treat glaucoma. It was later approved by the U.S. Food and Drug Administration as a treatment for eyelash hypotrichosis after clinical trials demonstrated increased lash length, thickness and pigmentation.
You can review the official prescribing information here:
https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/022369s014lbl.pdf
In the UK, the same active ingredient is prescribed under medical supervision rather than sold over the counter. Our in house doctors may prescribe bimatoprost if they feel it is a suitable solution to a client’s lash growth concerns.
Common Side Effects
Most side effects are local, mild and reversible. The most commonly reported include:
- Mild redness of the eye (conjunctival hyperaemia)
- Itching or irritation at the application site
- Dryness around the eyelid margin
These effects are typically temporary and often settle as the area adapts to treatment.
Studies demonstrate that 3 to 4% of people can have these side effects. In our own professional experience, we have found a lower incidence. We believe that focusing on applying as little liquid as possible, as precisely as possible, helps to significantly reduce the chance of any irritation.
Skin Darkening Around the Eyelid
Some users have noticed slight darkening of the skin along the lash line. It is usually mild, usually where you would apply eyeliner, and often reversible after stopping the treatment.
This occurs for two reasons; the first is that bimatoprost can stimulate melanocytes to increase melanin production. Secondly, the increased follicle activity requires increased local blood flow to support the enhanced growth.
In our experience since 2007, we believe that it is most commonly an issue when applying too much liquid and not applying it precisely.
Changes in Eye Colour (Rare)
One of the most discussed side effects is possible iris pigmentation change. This effect has been observed in glaucoma patients using bimatoprost eye drops directly in the eye.
However, it is very unlikely when applied correctly to the skin at the base of the hairs along the lash line. You are applying less than 5% of the amount used for glaucoma and little, if any, should get into the eye.
It is primarily a concern in individuals with mixed green and blue colour irises, and we have not seen it in any clients of Mylash since we began in 2007.
This is one reason why correct application and medical supervision matter.
What About Prostaglandin Analogue Lash Serums?
Some over-the-counter products marketed as lash serums contain prostaglandin analogues or derivatives, such as isopropyl cloprostenate.
These are not always regulated as medicines but they should be. The testing and safety data is not well established, leading to confusion over the correct dosing or usage.
The European Commission’s Scientific Committee on Consumer Safety has released a study recommending that they are banned:
https://health.ec.europa.eu/document/download/55295a0e-1aa8-4380-a8db-84ecf85b711c_en?filename=sccs_o_302.pdf
How Safe Is bimatoprost Overall?
In clinical trials and long-term use, bimatoprost has shown a good safety profile when used appropriately. Side effects have been shown to be rare and patient satisfaction has always been high. The key factors that make treatment safe are correct application, appropriate patient selection and medical supervision.
At Mylash, every patient completes a medical questionnaire reviewed by a UK doctor before treatment any is approved.
Who Should Not Use A BIMATOPROST TREATMENT?
Bimatoprost may not be suitable if you:
- Are pregnant or breastfeeding
- Have certain eye conditions
- Have recently had eye surgery
- Have a history of sensitivity to similar treatments
This is why a proper assessment is essential. We review your details to make sure that you are suitable, and you can ask our doctors any questions that you have.
How to Minimise Side Effects
In our 19 years of experience as of 2026, we have found that side effects are largely technique-dependent.
The most important points are:
- Apply only to the lash line or the eyebrows
- Use the smallest amount possible – the area should not feel soaked
- Avoid getting the product into the eye
- Do not apply to surrounding skin
- Wipe away any excess
- Keep consistent
- Only apply once a day – applying extra does not speed up or improve the results
Most issues arise from overuse or incorrect application.
TREATMENTS vs Lash Serums: A Safety Perspective
Many people assume that cosmetic lash serums are inherently safer. This is not always the case.
Prescription treatments like bimatoprost have been clinically studied, have defined dosing, are prescribed appropriately and are well understood.
Some cosmetic products contain unregulated ingredients, lack long term safety data and are used without guidance.
For many patients, a regulated medical treatment is the more predictable option.
Founded in 2007, MyLash was the first UK services to make effective lash growth treatments available in Europe. Our team has helped tens of thousands of clients achieve longer, thicker lashes under medical supervision.
We have been featured in multiple UK magazines and newspapers, recognised for our scientific approach to lash and brow growth.
Why Choose MyLash?
- Doctor-prescribed treatment
- Home delivery anywhere in the UK
- Established since 2007, trusted by thousands
- Featured in major UK publications
- Scientifically led, developed by Dr Tom Walker and run by a team of UK doctors
Frequently Asked Questions
The most common side effects are mild redness, irritation and itching around the lash line.
This is extremely rare when applied correctly to the lash line. It has mainly been observed in glaucoma patients using eye drops directly in the eye.
In most cases, skin darkening along the eyelid is mild and reversible after stopping treatment.
Clinical studies and long-term use suggest that bimatoprost has a good safety profile when used appropriately.
No. Often the non-medical lash serums use a modified prostaglandin. They are unregulated, banned in many places, poorly studied and can cause side effects.
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