Why IPL Sometimes Fails — And What Actually Works
If you're treating finer hair, dark skin, or hormonal areas, the physics of IPL may not be working in your favor. Here's what the science says.
Nearly a decade ago, I spent $200 on an at-home IPL device and returned it within a month. Not for lack of trying — I returned it because every flash above level 1 or 2 hurt enough that I had to stop and recover before continuing, and after weeks of trying, I had nothing to show for it.
I was a mechanical engineering student at the time, so “it just didn’t work” was not a satisfying answer. However, I didn’t have the framework yet to understand why it hurt that much and why someone with my skin tone and hair type was getting zero results while the device’s marketing showed nothing but smooth skin. That took years to figure out.
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Why IPL Devices Work Well for Some People and Poorly for Others
All light-based hair removal, “Photoepilation”, works on the principle of Selective Photothermolysis: light energy is absorbed by target tissue (melanin in the hair follicle in this case) where it gets converted to heat and destroys the hair-producing cells. Most at-home hair removal devices are IPL which stands for Intense Pulsed Light. The conditions that make selective photothermolysis work reliably for IPL are specific: pale skin and medium-to-coarse, shallow-rooted dark hair. “Dark” here means black or near-black — medium and lighter brown hair contains less melanin than most people assume and responds more like finer hair. Move outside the optimal conditions in any direction and the results drop off quickly.
Is Finer Hair Harder to Treat?
Yes, and the reason comes down to melanin. The volume of the hair determines how much melanin is present, and so by nature, finer hairs have less melanin to absorb heat energy than medium or coarse hair. Consequently, the heat generated at the follicle may not reach the threshold needed to permanently disable the hair-producing cells.
This limitation is even more pronounced with low-fluence devices. Because Fluence is a measure of energy density (J/cm²), a low-fluence device simply cannot produce enough heat to compensate for the smaller target. It essentially boils down to this: the thinner the hair, the higher the fluence required to treat it.
That said, not all fine hair is the same, and the distinction matters before picking up any light-based device. Terminal Hair is what actually responds to photoepilation. While it is usually coarse on areas like the underarms, calves, and bikini region, it can also be quite fine for some in areas such as the forearms and thighs. Vellus Hair, on the other hand, is the soft peach fuzz that covers most of the body's surface. Areas with only peach fuzz should not be treated with a light-based device, as doing so carries the risk of Paradoxical Hypertrichosis.
While peach fuzz should be avoided, areas with finer terminal hairs can effectively be treated if a device provides a high enough fluence to compensate for the smaller target.
Why Is It Difficult to Get Results On Hormonal Hair?
Deep-rooted hair found in areas such as the bikini region and beard presents a separate challenge. Hair in these areas is androgen-driven, meaning it is hormonal, and the hair follicles sit significantly deeper under the skin. To permanently disable a deep-rooted follicle, the device’s energy has to travel further through skin to heat the root to the threshold needed for destruction.
IPL devices in particular struggle with this for two reasons that compound each other. The first comes back to fluence: most consumer IPL devices don't deliver enough energy per flash to maintain sufficient heat that far below the skin's surface. The second is wavelength, which is basically the “color” of light. Different wavelengths of light naturally penetrate to different depths in skin — some deposit most of their energy near the surface, while near-infrared wavelengths travel deeper. Because IPL devices emit a broad mix of wavelengths all at once, the energy that penetrates into the skin is diluted across multiple depths at the same time, resulting in no single depth receiving a concentrated dose of energy.
Laser and LED-based devices that emit only a narrow range of wavelengths significantly reduce the energy dilution problem; most of their energy penetrates a certain depth into the skin, which happens to be where hair follicles actually sit. This makes them inherently more effective at targeting hormonal hair than IPL devices.
Dark Skin Compounds Both Problems
Skin tone adds another layer of complexity regardless of hair type. IPL devices emit a broad spectrum of light wavelengths, and melanin absorbs them without discrimination — in the hair follicle, but also in the skin itself. For darker skin tones which inherently contain more melanin, a meaningful portion of the device’s energy gets absorbed by the skin before it ever reaches the follicle. The classic “rubber-band snap” sensation that at-home devices are known to have is actually the skin absorbing heat it was never supposed to receive, which is why most IPL hair removal is more painful for those with darker skin.
For a full breakdown of the physics, I’ve covered it in detail separately: Why At-Home IPL Doesn’t Work for Dark Skin.
What Has Improved in the Last Several Years
Today’s IPL devices have improved on one thing: pain. Active cooling systems have made the experience more tolerable than what I used almost a decade ago, and for the right candidate — fair skin, shallow follicle depth, dark hair — some of today’s IPL devices can deliver real results. However, cooling does not change the melanin problem for lighter brown or finer hair, the depth problem for hormonal hair, or the fluence trade-off for darker skin. The underlying physics hasn’t moved.
When I went back to researching at-home devices, I wasn’t looking for a more comfortable IPL. I was looking for something that didn’t have those limitations baked in.
What I Use Now
I originally bought the ViQure S-LD with my own money after a lot of research several months before I started Science Over Fluff. As a person with medium-brown skin and relatively fine hair, I represent almost every challenge I’ve outlined in this article. I was also specifically looking for something that could handle deep-rooted hair in the bikini region effectively and without the extreme pain I’d experienced in the past.
The ViQure S-LD operates on a different principle than IPL. It uses a near-infrared LED source emitting wavelengths in the range of 780-850nm, selected to concentrate energy at the depth where hair follicles actually sit. It delivers 25 J/cm² of fluence (about 3 to 4 times higher than IPL devices), and the built-in active cooling makes that energy level tolerable to use. Because of this targeted approach, it is also effective for a broader range of skin tones (Fitzpatrick I to V).
After three sessions, I logged over a 70% reduction in hair in my treatment areas, so I posted a Reddit review about it that got a lot of attention. That is actually what inspired me to start this publication. I have documented my full experience with the S-LD (energy level selection, gel use, session spacing, and the effects that the first few treatments actually had) in a separate article.
Read more:
→ ViQure S-LD: Timelines, Hacks, and Real Results
Is This Right For You?
If you are only treating areas where you have fair skin and shallow-rooted dark hair, a modern IPL with active cooling may genuinely work for you. This article is for everyone else — those treating body areas with finer terminal hairs, hair in hormonal areas, lighter brown hair, darker skin, or any combination of the four.
Discount Code:
Did you find this article insightful? I was able to negotiate a reader discount on the S-LD directly with ViQure. You can get a good deal and support future content from Science Over Fluff at the same time by using the link and discount code below to make your purchase. Science Over Fluff earns a commission that funds future science-based content at no extra cost to you.
Disclaimer: While I am an engineer and enjoy breaking down the science of how technology works, I am not a medical professional. The information shared here is based on my independent research and technical analysis intended for educational and informational purposes only. Please consult with a qualified professional before starting any new treatments.
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