First, let’s separate the two folds of the crossing and call them Fold A and Fold B.

Very early in your life, Fold A and Fold B started meeting when you would do something.

At first, they probably did not meet at the exact same place every time.

As their paths became etched into your skin, under the action of the skin's wound healing process, so did the position of their crossing point.

A single road is quite rare on this planet.

A road will connect with another at some point, creating a road crossing.

We all know how much more action there is at the crossings than elsewhere on the roads.

The walls of both folds now crash into each other every time you do the same movement.

At the crossing point, the skin is badly and continuously deformed.

All this generates lots of heat.

Fresh epidermis cells, triggered by the skin's wound healing process, will come to the rescue of the poor crossing in order to prevent breakage or puncture.

One by one, coats of protective epidermis cover the crossing's center.

This action solidifies the skin of this mistreated region, but locks the crossing into place.

The corners of the crossing slowly close in and create a void in the center, a skin cavern.

This evolves height wise into a chimney-like structure.

Its inner passage is often constricted and twisted, with plenty of sudden curves.

The opening is often mistaken for a pore.

Some organic wastes, expulsed from the enclosed skin, remain captive inside.

The center of the fold crossing becomes almost completely encased into its sealed corners.

This structure solidifies, developing into a grotto made of skin.

At the top of the chimney, continuous refolding pulls more skin down into it.

The entrance gets covered and blocked.

But, most often, there remains an opening.

Since folds A and B are already grooves, not mounds, the fold crossing is often a hole.

As it evolves and fixates, it grows deeper and deeper below the surface of your skin.

The chimney starts forming.

The very top of the fold crossing keeps on refolding.

As time passes and your actions challenge it again and again, the top edge of the crossing adds new coats of locking epidermis to protect itself.

This brings new unfolded skin, next to the opening, into the chimney.

Sometimes, this relentless refolding forms a mound or agglomeration above the skin's surface.

They become jumbled messes of skin,

We notice the darker ones, but generally there is little color change. They could also be paler.

Epidermis formation often places a hard cover on the whole mass.

As the fold crossings on your body deepen, their connected folds also increase their depth.

This has the effect of thickening your skin gradually.

It is accompanied by a steady loss of sensitivity.

Most fold crossings are almost invisible to the naked eye.

They can be seen easily on your palm and soles, so you can observe a variety of styles with their branches meeting at every possible angle.

Some crossings are quite deep with redness visible in their center.

Some crossings grow in size while others simply tighten, most will do both.

At some point, the whole structure of the crossing may collapse and become part of a new, bigger one.

It can roll over itself.

A crossing can link with adjacent ones.

It can protect itself with a very hard cover.

A lock is a draping of the skin on one side of a fold crossing.

Like an accordion or a hand fan, they are made of tens, sometimes hundreds, of small folds.

Your skin’s natural horizontal and vertical folding tendency ends up creating a grid of folds and crossings.

Please note that the folds are not equally spaced like in the illustration.

In reality, the grid is variably spaced and complexifying, adding more folds (often diagonal) between existing ones as needs grow.

This grid adds new strength to your skin acting like a flexible skeleton inside of it.

It brings relief to large sections of skin between the folds.

The damaging pulling forces from your actions now travel down the branches of the folds up to the ever-growing crossings.

Tensions at one crossing are relayed to all the crossings in its vicinity.

The grid of fold crossings has several disadvantages;

•It greatly reduces the skin's flexibility and elasticity.

•On the face, expressivity and beauty are diminished.

•It interconnects problem areas. Doing one movement now affects regions further and further away.

•...

Because the size of your body has increased since your youth, the grid has tightened.

It is deepening into your flesh.

The folds and crossings multiply, enlarge and squeeze your skin still more.

This reduces your capacity to move, it makes anything you do more painful as you get older.