The Science of Hair Removal.
As I mentioned in the Lumea review, using the word "removal" for laser and IPL technologies is a misnomer. But everyone does it, so now that I've mentioned that it isn't correct, I'm going to do it too.
Both laser and IPL technologies affect hair in the same way. The difference between them is that laser light is coherent light with just one wavelength, while IPL is more like normal light - a combination of different wavelengths. You probably learned in school that the color of an object is determined by what wavelength of light it absorbs and what light it reflects. Something that appears black is absorbing all light, while something that appears white is reflecting all light. If an object looks green, then it is absorbing all but the green frequency of light, which gets reflected towards your eyes. Visible light has wavelengths between 400-700 nm (nanometers). 400 nm is the violet end of the spectrum and 700 is the red end. We can't see light which is outside of this range, but it can still be absorbed.
The substances that give molecules their distinctive colors are called chromophores. The chromophore that is responsible for hair color is melanin. Melanin absorbs wavelengths between 600-1100 nm, so the IPL flashes in devices like the LUMEA are filtered to provide just those frequencies.
As you can see, the cells with melanin absorb these flashes of IPL. The light gets converted to heat (just like your car seat in the sun) and this damages the hair follicle. Depending on the type of damage, the hair follicle might never produce hair again, or it might just stop for a few weeks.
Note in the picture above that the hair above the skin will be absorbing the light as well. That heat won't affect the hair follicle, but it could be a bit painful, so this is why you need to shave or epilate before you use IPL.
This process, of light converting to heat and damaging the hair follicle is called photothermolysis. Photo means light, thermo means heat and lysis means "to cut," so that means 'cutting' with light generated heat.
Melanin is also responsible for skin color. Your skin has a different shade of melanin than your hair does and for the best results, we want our IPL devices to target only the hair's melanin. Targeting only one color of melanin is called selective photolysis. Light hair won't absorb much light at all, so we need darker hair. And IPL (or laser) will work its very best when there is a big difference between your skin color and your hair color. So fair skin and black hair are the optimal candidates for laser or IPL hair reduction because the hair absorbs all the light and the skin none at all (or very little).
What happens to the hair?
The hair follicle is a pocket in your skin which builds the hair shaft and controls the hair growth cycle. Here's a hair follicle:
There are four zones:
- Dermal Papilla fibroblasts. This is at the very base of the follicle and provides blood and nutrients.
- Hair Matrix with Matrix keratinocytes and melanocytes found in the hair bulb.
- Bulge with epithelial stem cells.
Not all of these contain melanin. So what happens is that the cells with melanin get heated first. These are the melanocytes and keratinocytes in the matrix, along with the keratinocytes found in the shaft. Then the heat moves from these cells to the non-pigmented cells. The cells that are most important to affect are:
- Dermal papilla fibroblasts
- Epithelial stem cells in the bulge
- Matrix keratinocytes.
The dermal papilla fibroblasts and epithelial stem cells communicate to trigger the hair follicle's cycle of growth.
The Hair Growth Cycle.
This picture shows the stages of hair growth. The actual duration of the cycle differs by body area, but the cycle is otherwise the same:
- Anagen or active growth: The dermal papilla attaches to the hair follicle and the hair starts to grow as cells divide and multiply in the hair bulb.
- Catagen or end of growth: the follicle and hair fibers retract from the dermal papilla and stop growing.
- Telogen or follicle inactivity) the hair follicle is inactive and the hair eventually falls out or is pushed out by new hair growth.
If we damage the dermal papilla fibroblasts and/or epithelial cells with enough heat, they breakdown. This damage is irreversible and the result is that the hair follicles miniaturize. In the next growth cycle no hairs grow at all, or at most soft vellus hairs grow. These are so fine and light it seems as if nothing is growing.
On the other hand, if we damage the matrix keratinocytes, this causes the hair to jump to the Catagen stage. So the hairs stop growing and will fall out eventually after a few weeks. This is gives the quick, smooth skin results. But if we only damage the matrix keratinocytes, the hair will still grow back just as always. The dermal papilla and hair bulge cells are still fine and will trigger hair growth. It's the goal of IPL and laser hair treatment to target all three of these cells for long-lasting hair reduction.
The Growth Stage Matters
To be successful, you have to nuke hairs in the Anagen stage. This is when the follicle builds the hair rapidly and there are lots of melanin-rich cells. And remember that the dermal papilla is only attached to the follicle during the Anagen stage (see the picture, above). It's the only time that you can really get heat from the hair to the non-pigmented target cells and dermal papilla.
Since hairs all over your body follow these cycles but at different times, you need several IPL/laser sessions at regular intervals so you can eventually nuke all the hairs during the Anagen stage.
Home IPL: It's not quite the same
Home devices are not as powerful as the ones that you get at professional hair removal clinics. Home devices do not reach all the way to the dermal papilla fibroblasts. Instead, they primarily damage the matrix keratinocytes. This causes the hair to jump to the Catagen growth stage and the hairs stop growing and fall out. But this also means that if you don't keep up treatments, the follicle will enter a new Anagen stage and grow back just as before.
However, if you continue treatments, you will gradually also damage the dermal papilla fibroblasts and the stem cells int he hair follicle bulge. Eventually, if you keep the treatments up, these will become so damaged that they can't produce new hair and the cycle is broken. There are some studies that suggest that if your maintenance sessions can continue for about a year, every six-weeks or so, you can achieve high and long-lasting hair reduction (up to almost 85%) for up to 1-year after stopping the sessions.
This is why the phase-two sessions are so important. And your results should continue to get better and longer-lasting the more you use the device. Based on this, you will probably need between 12-20 sessions in your first year of home-use. Not so bad to be hair-free!
If you have questions and, especially, if you try out the Lumea, please get in touch with me and let me know how it works out for you. To do that, you can message me on Twitter