-Some Methods of Quantifying Experimental Results and

Estimating Cosmetic Implications for Home Experimenters-

Hi Guys,

Here are some notes I would like to share with other

DIY Follica experimenters.

Thought I should write this stuff up; maybe you can

use some of the methods I’ve been utilizing, and

perhaps there is use for a thread on this and we can

pool some ideas there.

Included below are methods for determining hair

diameter and density (under certain conditions) using

readily available items, and some derived and collected

methods of estimating cosmetic implications of known

densities and diameters.

Here goes…

Since I’ve been seeing at least some results from a

combination of things I’ve been trying, it occurred

to me to ask the questions:

What type of regrowth would be required to produce

cosmetically significant effects?

How can I measure/quantify the results I am seeing?

If I think I am seeing results from my experimental

treatments, can I estimate/predict the cosmetic

implications of my results?

Assuming results are repeatable, how many treatments

would be required to achieve the cosmetic results I

desire with the particular method I’ve been using?

After reading a lot about this (it appears these are

really important questions when performing HT’s, so

they’ve been explored extensively for that purpose),

some of the most important factors appear to be:

-Density of hair (most commonly measured in number

of hairs per square centimeter) Individual hair

densities vary depending on a number of factors

but typically are around 200 hairs per square

centimeter.

-Average diameter of hairs (this plays a big role

in how much hair is required to produce cosmetically

significant results, thinner hair shafts requiring

more hair, thicker hair shafts requiring less)

This generally varies on an individual basis also,

in the range from around 20 to 200 microns.

-contrast between hair color and scalp color

(lower contrast here means less density is required

for good cosmetic results, higher contrast means

more density is required)

The last factor is inherently qualitative; however,

surprisingly, recently available technologies appear

to allow us to get good estimates for the other two

factors (see below for a discussion of this).

I was first trying to figure out how to

mathematically estimate the cosmetic implications of

particular combinations of the first two factors.

From the literature, it’s generally stated that

hairloss is first noticed once hair density

decreases to about 50% of it’s original value.

Since this value is roughly around 200 hairs per

square centimeter, one might conclude that a

pretty good restoration target for the average

individual would be around 100 hairs per square

centimeter.

I explored some other methods for predicting

"good" density targets:

As an initial first model, I tried to figure

out how many hairs of a particular diameter

and length would be required to completely cover

a field of view, assuming they were all lying

flat and aligned side by side (this is an

optimistic model, but it seems like it should

allow a good estimation of a lower limit for the

requirements). The exact equation I came up with

for this simplistic model is:

required density in hairs per square centimeter =

10000 / (hair length in cm * hair diameter in microns)

This is a lower limit, because it assumes the

hairs are lying side by side, and they are flat

in the field. In reality, the hairs obviously

rise off the scalp, and overlap each other in a

three dimensional region. On the other hand,

absolutely complete coverage is not necessarily

needed for the illusion of density, but maybe this

simple model is a good starting point.

I’ve measured my hair diameter to be on average

about 50 microns (I outline later a for method

for measuring this yourself). So for example,

in this simple model if hair were 3 cm long,

10000 / ( 3 * 50 ) = 66 hairs per square centimeter

seems a bit low, but certainly a lower bound…

I then did some searching, and found this

fascinating way to estimate the cosmetic effect

producible given particular diameters and densities:

For those interested in this topic, Dr. James

Harris presents a fascinating system for

making estimates at this link:

http://www.hsccolorado.com/news_events_research.asp

Here, he describes a way of calculating a number,

which he calls the HVI (Hair Volume Index) which

he correlates with the subjective visual hair

density given an individual’s particular density

and average hair diameter.

Essentially, his equation is:

HVI =

hair diameter in microns * hair density in hairs per square centimeter / 100

which he relates to the following subjective ranges

thin appearance: HVI < 20

moderate appearance: HVI 30 to 40

dense appearance: HVI > 60

For instance, given my current measurements of

density (around 50 hairs per square centimeter)

and diameter (around 50 microns), I would

calculate:

HVI = 50 * 50 / 100 = 25

To boost this to the “middle moderate” range

by increasing density, I would need to increase

density to:

hair density in hairs per square centimeter =

35 * 100 / 50 = 70 hairs per square centimeter

For “dense appearance”, I would calculate:

hair density in hairs per square centimeter =

60 * 100 / 50 = 120 hairs per square centimeter

(this might also be useful for those

considering HT’s and trying to estimate how

many hairs or grafts would be required to produce

a particular result)

So, now equipped with some methods of

predicting what the cosmetic impact of a given

density and diameter would be, how can these

quantities be measured? Surprisingly, there

appear to be a few methods which can yield

considerable accuracy available to us.

For density measurements, I have been most

successful using a digital camera with macro

focus and little strip of plastic cut to 1 cm

in length.

I’ve had the hair cropped short so it’s easy

to identify individual hairs once a photo is

taken of a region of the scalp. The plastic

strip is placed on the scalp within the field

of view of the photograph as a scaling

fiducial. When the photograph is examined,

hairs can be counted within any square region

having the same width as the 1 cm wide plastic

strip. In other words, I can zoom way in

until the plastic strip fills the width of

the field of view, and then pan around in the

image to estimate haircounts at any location

in the image.

That’s the best I’ve been able to come up with

for home methods of estimating density.

For measuring hair diameter, you can actually

do this quite accurately at home using a

laser pointer! I have done this and it does

work. Be careful not to point the laser

directly into your eyes, of course.

I tape a sampled hair across the beam where

the laser emerges from the pointer, then

point the beam at a wall a few meters away.

The laser light diffracts around the sides of

the hair forming a diffraction pattern which

basically looks something like this:

— — — —*--- — — —

The pattern is the brightest in the center of

the beam. I could write a lot about the

science behind this, but if you are just

interested in using the method to measure

hair diameter, what you want to do is measure

the distance between the pointer and the wall.

Then take a piece of paper and place it on the

wall on one side of the pattern and mark

the location of the minimum intensity points

in the lines which extend out to the side (the

places where it’s the *dimmest*).

Then take the paper and measure and figure

out the average distance between those

minimum points.

Then, use this equation to determine the

hair diameter:

hair shaft diameter =

laser wavelength * distance between hair and image

/ distance between minimum intensities

If you are using a red laser pointer, your

laser wavelength is 650 nanometers or

650 x 10^-9 meters. For example, say you

measured 1.5 meters between your laser and

your wall, and you determined the average

distance between your minimum diffraction

pattern intensities to be 1.4 cm

(or 0.014 meters).

Then the diameter of the hair which produced

the pattern would be:

diameter of hair =

(650 x 10^-9) * (1.5) / (0.014)

= 0.0000694 meters

or approximately 70 microns.

Because of variation in diameter really

necessary to do this for a number of

hairs and average the results if you’d

like to get a good idea of the average

diameter.

See the following links for in-depth

discussion of this method and the theory

behind it, some useful photos, etc. :