If I had to sum up some of the most frequently asked questions on TIA, they are mostly about eyebrow and eyelash growth and they run along the lines of:

Will over-plucked eyebrows ever grow back?

Why did my eyelashes start falling out when I started to use a growth product?

Will I have to use these growth products for the rest of my life/What will happen when I stop?

How long before I see results?

There isn't a short answer to any of these and I am afraid that they require at least some understanding of how hair growth works: yep, it's time for hair growth 101.

The hair growth cycle

All hair - whether on the head and brows, the eyelashes or the unmentionables - grows in phases. There are three of them, to be precise. The only thing that differs (from, say, lash to head hair) is how long the phases take. But we'll come back to that.

Anagen - the growth phase

Each follicle can grow many hairs over a lifetime: on average, each grows a new hair around twenty times. The phasing of the growth cycle is staggered amongst the follicles. Which prevents us from periodic phases of baldness when the growth cycle stops.

The growth phase is called anagen. How long anagen lasts is determined genetically, and varies between the sexes and from one person to another. It is the length of this time that determines how long the hair will grow. For head hair, the anagen phase can last from three to as much as seven years.

Fun fact/myth buster: It is not true that cutting your hair makes it grow faster or thicker. Nor does shaving your legs make the hair grow coarser. The length of the growth phase and the width of the hair shaft are the results of your genes, and are not affected by anything you do to your skin or to the hair shaft itself.

Catagen - the intermediate phase

The anagen phase is followed by a short resting phase. This catagen phase lasts between two and four weeks. No pigment is made during that time, and the follicle stops producing hair. The base of the follicle moves upwards towards the surface of the skin.

Telogen (the shedding phase)

The telogen phase lasts for three or four months. During this time a new hair begins to grow from the hair follicle. As it grows upwards the old hair will be shed naturally or may be pulled out. Tweezing is easily and painlessly done with telogen hairs. These are the hairs that come out when you shampoo or brush your hair.

Shedding is part of the normal process of the replacement of old hair with new. At any one time, around one in ten of the follicles on an individual's head are in the shedding phase.

The new hair emerges from the same opening at the surface of the skin as the old one, and the hair cycle begins again.

As people age, the hair cycle can become shorter (this isn't true for everyone and depends on your genes). The follicles gradually give up producing long, strong hair, and the hairs become thinner and shorter. This can happen to lashes, brows, leg and arm fuzz and so on.

What's different about lashes and brows?

Not much. Eyelashes shed just like head hair. It may be that people who think their new eyelash growth product is causing their lashes to shed are nothing more than the victims of coincidence. On the other hand, it could seem to be a more dramatic loss than normal. This could be due to the fact that some eyelash growth products, specifically the ones that contain prostaglandins, speed up the growth cycle prompting a bout of shedding.

The growth cycle of eyebrows and eyelashes are a mere blink of the eye compared to head hair. Eyebrows take up to 64 (give or take) days to come back fully. Eyelashes are even more fleeting, taking only four to six weeks to come and go.

Follicles - the growth engine

Each individual hair is formed inside a hair bulb deep in a hair follicle. The follicle is a tiny but powerful factory. Although some male balding is due to testosterone, there is a growing understanding of the role the follicle plays in other kinds of hair loss (female hair thinning, sparse lashes and brows). A healthy follicle apparently produces nice strong hair.

If you pull a hair out of a follicle another one will grow up in its place. Not so, say some of you: "I over-plucked by eyebrows during the 80s when I didn't know better and now they won't grow back."

I'm not sure if the over-plucking theory is no more than urban myth, but I couldn't find any hard evidence to support it. What I did find, over and over again, were unsubstantiated statements along the lines that over-plucking causes follicle damage. How? Look at the diagram: the follicle is snuggled below the epidermis and the root is way down. Unless the tweezer is used as a probe, I don't get it.

Furthermore, more scientific references I have come across say that there isn't much environmental damage that can be done to a follicle that would stop it producing hair. There would have to be severe physical damage such as burning or scarring to achieve that.

Some (tentative) answers to the FAQs

Over-plucked eyebrows should, theoretically, grow back if the follicles are given some TLC (which is what products such as Brow Vitality Complex ($36 in the shop), with copper peptides and emu oil, are supposed to do). I regularly (approximately every other day) apply Brow Vitality Complex and my once-moth eaten brows are nicely filled in and the hairs are darker and thicker.

You do have to resign yourself to continued use of these products if you want to continue to have results. When you stop using an eyelash growth product, your growth cycle will revert back to normal. Plus, you may (depending on your age) need to counteract the post-42 thing.

As far as results go, this will vary from each person because of the genes that gave them their follicles and dictated the length of their growth cycles. And if you are lucky enough to start using a product during the telogen cycle, you might see results more quickly because you were just about to go into a growth period anyway.

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