Folded skin theory

Let's first put together graphically what we've seen in the previous chapter.

A longer span of unfolded skin would look like this.

Now, let's fold it.

Both sides of the fold become walls, facing each other.
They are held together by a filling composed mostly of hardened epidermis coats.

Trapped skin

Part of the skin becomes engulfed into the fold.
Some hair follicles and sweat glands remain trapped inside, their exits are blocked.
Their vital functions, hair, sebum and sweat production, are halted. It is like if time was suspended for them. Hair stops growing and doesn't even whiten. Once freed by grooming, they spring back to life.

 

Fold evolution

Folds have phases in their evolution.
At first, they are not etched into the skin, then they slowly solidify, deepen, harden, tighten and multiply.

First folding

Let's try to imagine how unfolded skin reacts to a folding movement.
Please picture a theoretical virgin wrist.

-When the wrist is at rest, there is no fold.

-When flexing begins, the fold starts out very short and shallow.

-As the flexing accentuates, the fold lengthens and deepens.

This ideal skin would bounce back to its unfolded state as soon as the wrist is straitened.

Damage due to repeated folding

If your skin was to be folded only occasionally, of course no damage would occur.
But think of how often you wink, swallow, talk or eat and you’ll understand that folding represents a real challenge for your skin.
You know the impact folding has on objects. You probably fold some things repeatedly to separate or divide them.

How damaging the process is depends on:
-The rigidity and elasticity of the folded material.
-How long you do it.
-At what speed.
-What vigor is applied.
-...

When repeated folding occurs, heat builds-up on the floor of the fold.
The structural integrity of the material is put to test and some is mutilated in the process.
Luckily, skin is unbelievably flexible and elastic.
It can be folded thousands of times without damage.
Still, when things get real hot, your skin has to protect itself.

Heat due to repeated folding
and epidermis formation

The heat buildup triggers specific epidermis formation into action.
There are two hot areas:
-The floor of the fold.
-At the two fold endings or break points.
The skin knows it has to do something to protect itself at those spots or it risks rupture or perforation.

Coating the fold’s floor

While the repeated folding is occurring, the excess heat is concentrated all along the path of the fold, on it’s floor.

In reaction, the skin will pave the bottom of the fold’s route with a fresh coat of epidermis.

Endings breaking into the skin

If you return to the first folding illustrations above, you can see the fold lengthen as the movement accentuates.
This creates a breaking wave as the fold's endings crash into unfolded skin.

The skin deformation involved in these two areas produces extra heat thus forcing the production of epidermis.
With time, this action will keep both ends of the fold closed. The endings become invisible.

 

Fold structure

A fold is a groove in your skin, an inward indentation. Once closed, it is similar to pinching it, but from inside of you.

Fold variables

Folds have several variables that differentiate one fold from another. Here is a short list:
-Location: Where the fold is situated on your body.
-Orientation: General direction of the fold.
-Length: Even though most folds go around your body or part of   it, a movement you do may only affect part of it.
-Depth or amplitude: The magnitude and intensity of the fold   causing movement will affect its depth. It is likely to be at its   deepest in the center, but has a relatively equal deepness all   along its floor except at the endings.
-Path: Most folds illustrated in this book are drawn straight.   Folds have a tendency to go in straight lines, but your nail will   reveal their very complex path.
-Fold closing: How closed a fold is depends on the angle its   walls have compared to the skin surface.

  Generally, a fold is more closed at its extremities than in its   middle section.
-Fold angle: In the preceding examples, the folds are   perpendicular to the skin’s surface, but most folds are angled.   In many cases, the walls of the fold become almost parallel to   the skin’s surface.

-Fold rotation: The walls of a fold may curve up to the point   where the fold rolls over itself.

A fold can roll on itself several times

Anchoring

If a fold meets an obstacle on its path, such as a bone beneath the skin or simply another fold, a new hot spot is created.
The epidermis formed at the point where the fold and the obstacle meet will slowly link and attach them together.
This phenomenon greatly reduces the skin’s mobility causing an anchoring effect.

Surface folds

When you become an adult, most of the deep folds are already in place.
Your skin is now so thick and tight that it couldn't be be folded entirely anymore.
The folds that develop after that only bend the surface.

How long is a fold?

Folds go for as long as they can.
If you create a fold, in most tissues, it has a tendency to prolong itself from one edge to the other.

Circular articulation folds

The skin of many parts of your body is tubular.
Fingers, arms, legs, neck, trunk, ...
All these tubes are vertical.
Some sections along them cover articulations.
These articulations work only one way and do not permit flexing in the opposite direction.
This means the skin tubes are always bending on the same side.

Compressed and stretched folds

This situation creates two types of folds:

Compressed folds tend to be few in number, but deep.
The skin really gets folded.
Stretched fold are small and numerous.
Both types meet on the sides of the tube, creating circular horizontal folds.

 

Epidermis coats inside a fold

Over time, specific epidermis formation will come into action several times on the same fold.
Coat after coat, the structure of the fold evolves.

Coats and cyclic activities

You do things, then you stop doing them.
Even continuous human activities, such as your heartbeat and breathing, are cyclic.
You wink only during the day.
Your weight is on your back only at night.
You may do some things once a day, on week-ends only, once a month, ...
In some occasions, you may perform these activities with much more intensity, speed, stamina and stress or for a longer time.

Fold coat creation

Each time the fold’s integrity is challenged by your activities, it adds a new epidermis coat to its floor and closes its endings.

Folds growing inward

Since the fold is a groove, it deepens into your skin as new coats are added.

But each time this happens, the fold finds a new, evolved situation.
Conditions have changed slightly.
Each point in the fold experiences changing pressures, and these affect the shape of its growth.
This results in a different epidermis structure for each new coat.
As their number increases, unfolded skin at the top is pulled down, and the whole edifice deepens into the flesh.

A complex path with irregularities

As a consequence, most folds grow hundreds of coats.
Their path becomes incredibly complex. It gets twisted and may roll over itself partly or completely several times.

Coats and grooming

When you groom a fold, it unfolds coat by coat.
You can feel each coat yielding beneath your nail.
This is due to the fact that each coat had time to dry before the next one was produced.