• Audrey Davis-Sivasothy is a Houston-based freelance writer, health scientist and consultant to the cosmetology industry. She is the author of two hair care books—Hair Care Rehab: The Ultimate Hair Repair and Reconditioning Manual and international beauty market bestseller, The Science of Black Hair: A Comprehensive Guide to Textured Hair Care.

  • Audrey

Terminal Length and Genetics

Terminal Length and the Role of Genetics in Black Hair Care

What is Terminal Hair Length?

Publish Date: 02/15/2009

So you’ve been taking care of your hair diligently for the last year. You’ve been protective styling, reducing the heat, and taking care to address your protein and moisture concerns as they arise from time to time. You’ve changed your old habits, and at first your hair seemed to take off – greatly improving in health and length. Then you hit what seems like a growth plateau. All of a sudden, the dreaded “T” word comes up: terminal length.

Or . . . I’ve heard it a million times.

Well I am genetically predetermined for shoulder length hair because my hair has been this length for my whole life. And come to think of it, so has everyone else in my family . . . it is genetics.Again, the dreaded “T” word comes up: terminal length. Then, upon close examination of their hair regimen (or lack of one) you find that they are still frying, dyeing, and not actively tryingto grow their hair. Improving the length and condition of the hair obviously does not happen by accident, but where do genetics and terminal length come into play?

Why does my hair stop growing at a certain point?
For most of us, growing the hair without actively taking steps to maintain it, often ends in utter disappointment; but then sometimes, even excellent care has us wondering why we appear to be making no progress at all. Many factors go into dictating whether or not a person will be able to achieve a healthier, lengthier head of hair. It is very easy at this point to give up and concede your lack of growth to genetics or some other factor, but before you throw in the towel—take these notes into consideration. Let’s talk terminal hair length and genetics!

Terminal Length
Each month, your hair grows at a certain rate that may increase or decrease slightly from month to month. This rate is typically 1/2 inch per month: slightly faster for Asians and Caucasians and closer to average or just below for those of African descent. This regular monthly growing happens for a number of years for each strand of hair on your head. Each strand has its own sort of timetable set around this. Both your monthly growing rate and your total growing period, or phase, are determined to a large extent by your genetics. Environmental and personal health factors may also influence both rates.

Your terminal length is the longest length that any hair on your head can grow given your monthly growing rate and the length of your growing periods. Simply put, terminal length is the length that your hair would reach if it were never cut, never broke, and was just allowed to grow freely without interruption. Once a hair has completed its total growing period and has reached its terminal length, it will shed naturally and be pushed out by (or eventually be replaced by) a new, growing strand. This process repeats all over your head, day in and day out, for your entire lifetime for each single strand of hair.

Hair that has reached its terminal length tapers naturally into this position. Hemlines that have reached terminal length are rarely blunt or even because different strands of hair are at different points in their life spans and rarely reach terminal length together. *(If all of your strands of hair reached terminal length together, your hair would fall out all at once, you’d be bald for a few weeks, and then your hair would start growing in all at the same exact time. Not a good look.)

It’s not about length, it’s about TIME.
Now, there’s a very important point to be made. You often hear people say “Well, my hair grows to (insert length here) and stops, so this must be my terminal length and genetics. This is not completely true. ” Your particular hair length does not determine when your hair stops growing or goes into resting (telogen) phase. TIME does. Our hair doesn’t stop growing at a certain length—it stops growing after a certain time period. Again, this is where genetics comes in. This time period, or growth phase, is set by genetics with the average growth phase for hair on the head being 2-6 years for humans across racial lines. Some of us have longer phases, some have less. And, this is where the terminal length argument can get tricky. While terminal hair length is determined by the amount of time a hair has been growing overall, the argument logically follows that if left to grow undisturbed (no breakage/cutting), terminal length does eventually translate into a particular length of hair. Unfortunately, many of us have not been growing our hair long enough under very healthy hair conditions to see our strands reach and be maintained at our true terminal lengths for any given period of time. Some of us have old, beat up hair from our pre-hair care days that will need to shed and pass on before our hair stands a chance of reaching within the bounds of our terminal hair length. Others of us prefer neat hemlines to our ends and length, and so the regular trimming and touching up will prevent us from seeing our full length potential.

I am willing to go out there with almost 99.9% certainty and say that shoulderlength and APL (armpit/arm crease length) are hardly anyone’s terminal lengths. If growth cycles range from 2-6 years, then the woman with the shortest growth cycle of two years can expect her hair to reach 12 inches in length before the hair will shed- assuming she has not trimmed or lost any length to breakage. Thanks to the spherical shape of the head, for many of us, 12 inches measured from the nape and ear area on down will equal at least brastrap length. For women with longer growth cycles, waist length and longer lengths are not uncommon terminal lengths. Most experts agree that a terminal length of between 1 and 3 feet is typical.

You often hear arguments about whether or not terminal length actually exists. It does! All hair on your body is subject to predetermined genetic growth and resting phases. Your eyelashes, arm, and leg hairs go into a resting phase within a few months after the onset of growth. This is why this hair doesn’t get very long whether you shave it or not. Just like the hair on your head, the hair follicles on your arms and legs do not go into resting phase as soon as the hair hits a certain length. They go into resting phase when their growing time frame has expired- which may correlate with a certain length when experienced over time. Without terminal hair lengths, and some type of order to our growth, we’d be braiding our arm and leg hair.

To sum it up– if your growth cycle happens to be 4 years for your head hair, no matter how long your hair is at that point it is going to be shed at that 4 year mark. You could either have gained as much length as your growth rate will allow you to gain within that 4 year time period… or you could shave it bald at 3 years and 355 days in and it will still shed at that same 4 year expiration date. Your job is to make the most of your 2-6 year growth phase! Obviously, things like age, poor health, and bad hair care practices can cause hair breakage or growth cycles to shorten in length.

How Do You Determine Your Terminal Length?
I believe that most black women have never achieved their terminal hair lengths, nor have they seen mothers, aunts, or sisters do it. Neither have I. Years of bad or nonexistent information on black hair care have put many of us at somewhat of a disadvantage. For determining possible genetic predisposition to short hair and terminal length, you would really need to look at the hair care practices of all of the women in your family over the course of a few years. Before you do this; however, you must make sure that every one of them is practicing impeccable hair care methods. By impeccable hair care, I’m talking a no heat, no coloring, natural, low manipulation, protective styling regimen. If after 4-5 years of impeccable hair care methods, these women still have not seen brastrap, waist-length, or close to it, then genetics might be a factor. The point of this whole hair journey is to break the cycle of doubt and find out our true hair potential once and for all.

Your terminal length would best be decided on a fresh hair that started growing the day you started really caring for the health of your hair. You would need to follow this hair for years until it is eventually shed to truly know the terminal length you can expect. Now you are thinking- It is virtually impossible to follow a single hair from “birth to death”! And you are absolutely right! It is next to impossible to know your terminal length unless you’ve been growing your hair steadily for many, many years under the absolute best conditions.

You also cannot expect to use your current head of hair as a judge of terminal length for some time, especially if your hair has been put through the ringer! The hair you already have on your head has already probably been growing for years in its own cycle with each individual hair working on its own specific timetable. Additionally, this already aging hair has most likely not received the best care before this point. Let’s say your growth phase is 4 years. You have about 4 years to grow your hair as long as it will grow before it sheds. If 3 of those years of the hair’s “life” were spent not being cared for, the growth gained in the last year of its life may not seem all that significant. As it has grown, it has been subjected to damage and breakage through the years, so your “terminal length” can appear to be as short as shoulder or neck-length for a period of time. By the same token, a hair that is “born” during your healthy hair care days stands the better chance of reaching your true terminal length as opposed to the older hairs around it. The point is, you do not know how old each hair is or what type of breakage it has already endured to this point. This is why when setting your length goals and determining terminal length, you can’t simply expect to add, or more correctly, uniformly add length to your hair all over either. Some of the hair you are looking at now may be weeks away from the end of its growth journey. This is why it tends to take a little longer to reach certain lengths with fullness through to the ends. These transitionary hair phases are what I believe to be the cause of the “growth plateaus” or standstills that can happen in the best of hair regimens.

The Dreadlocks Question
In discussions about length potential, you often hear folks bring up the fact that dreadlocks grow so long that they must be a testament to the great lengths that we can achieve. I believe in the potential of every black woman to grow their hair to amazing lengths, but dreadlocks are not a good example in this case. While it is true that dreadlocks can and do reach great lengths, there is also a catch. Dreadlocks are unique in that they do not represent true “root to ends” length. They are the accumulation of shed, broken, and growing hairs matted together. Imagine if all of the shed or broken hair you ever had in the span of a year or in a lifetime were woven together! You too would have hair well down your back. This is the science behind loc’ing. Those hairs that are dropped are “locked” into your locs.

Interestingly, there is a process by which locs can successfully be undone or unloc’d, preserving quite a bit of the natural length. But much of the hair is still lost to the process at the end of the day, and waist length or floor length locs simply do not translate into waist length of floor length loose hair.

Optimistic, yet Realistic
Some of us do have it easier than others it seems, and genetics may be at play– but I have yet to see a strong, focused regimen fail to deliver on its promises over time. If years of healthy hair care have not produced hair growth beyond a certain point or healthier hair in general, before you chalk it up to genetics, a regimen re-evaluation may also be in order. What works with your shoulder-length hair, may not work for your brastrap or longer length hair etc. Also, look at your overall health— are you getting the nutrients you need? Are you drinking enough water and exercising? Are your nails healthy? (Our nails can give us a clue about the actual scalp nutrition our hair is receiving from our blood supply that feeds the roots. )At the end of the day, you must evaluate your long term hair care methods to see if they are conducive to growing and maintaining YOUR own hair.

Unfortunately, the chances of you growing your hair out to floor-length are slim to none- and Slim just walked out the door. Hair this length has been growing for more than 6 years in its growth cycle; and though it can be done (I’ve seen it!), it is difficult for most people to grow their hair to this length. Since the hair is older, it will take lots of time and amazing dedication to perfect a regimen that will sustain hair at this length. While lengths like tailbone, knee, or thigh length may be ambitious for many of us (and definitely require a bit more optimism), brastrap length and waist length hair are not that long for us and are certainly within our reach! These lengths are not some unobtainable dream! Do not be discouraged ladies, we can do it. As more of us learn the proper hair care methods for our hair, we will begin to see more and more of our sistas sporting lengthy tresses- natural and relaxed.

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