The mechanical argument
Think of the stratum corneum as a laminate: layers of flattened cells bonded by ordered lipid sheets and by protein connections between the cells.
Wet it, and the cells absorb water and swell. The laminate expands unevenly, because the cells swell more than the lipid between them. Dry it, and everything contracts again.
Do that once and nothing much happens. Do it fifteen times in a day, every day, and you are applying a repeated strain cycle to a bonded structure. Bonded structures fail under repeated strain in a characteristic way: the bonds go first.
That is why the picture in hands subjected to a lot of wet and dry cycling is one of disordered lipid sheets and loosened cell to cell connections rather than of a layer that has simply dried out.
Why occupational guidance counts events
You do not have to take a mechanical analogy on trust to see that this is how the problem behaves. Look at how work related skin problems are approached.
Occupational guidance on wet work does not simply ask how many hours the hands were wet. It attends to how often hands are wetted and dried, how often gloves go on and come off, and how often washing occurs. The Health and Safety Executive publishes material on skin at work and on preventing work related dermatitis that treats frequency as a controllable exposure with employer duties attached.
The pattern that produces the most trouble is not the fisherman with wet hands for four hours. It is the person who washes, dries, gloves, ungloves, washes and dries again, thirty times in a shift.
The version this readership has
For someone in cold water sport, the cycling looks like this on a Saturday.
Wet suiting up in a car park with rain on your arms. In the water for ninety minutes, so wet throughout. Out, into wind, so drying fast while cold. Peeling the suit, so wet again from the inside. Towel, so drying. A rinse, so wet. Drying in the wind while getting changed. Driving home with the heater on, so drying hard. A shower at home, so wet and warm. Drying again. Washing up after dinner, wet and dry three more times.
That is around ten full transitions in a day, several of them with the skin cold and several with a mechanical load applied while the layer is softened. The total time wet is not the number that matters.
Why the transitions are where the damage happens
There is a second reason transitions cost more than either state, and it is the one people can act on immediately.
A wet or recently wet stratum corneum is softened. Its cells are swollen and its bonds are under strain. In that state it is much easier to remove cells mechanically than it is when the layer is dry and settled.
What happens at every transition from wet to dry, in real life, is that a towel is applied. Or a wetsuit is peeled over the skin. Or a glove is dragged off. Or the skin is rubbed to warm it up. Every one of those is mechanical work applied at exactly the moment the layer is least able to resist it.
That is why blotting instead of rubbing is not a fussy piece of advice. It is the single highest value change available at the moment of maximum vulnerability.
| Moment | Transition | Mechanical load applied at the same time |
|---|---|---|
| Suiting up in the rain | Dry to wet | Pulling neoprene over damp skin |
| Ninety minutes in | Wet throughout | Seams and collar moving |
| Out into the wind | Wet to drying | None, but drying fast while cold |
| Peeling the suit | Drying to wet | Considerable, and on softened skin |
| Towel | Wet to dry | The highest of the day, usually |
| Rinse | Dry to wet | Low if you blot |
| Changing in the wind | Wet to dry | Clothing over damp skin |
| Driving with the heater on | Dry to drier | None |
| Shower at home | Dry to wet and warm | Towel again afterwards |
| Washing up | Three more cycles | Scrubbing |
Ordering framework written by this publication from general skin physiology. It is not a measurement, it is not taken from any study, and no number in it is a reading.
Reducing the number of transitions
Once you count transitions, some of them turn out to be optional.
Do not wash your hands and then immediately do a wet task. Do the wet task, then wash once at the end.
Put gloves on dry hands and leave them on for the task rather than removing them repeatedly. A glove that goes on and off ten times has created ten cycles.
Do not rinse, dry, change, and then shower. Pick one. If you are going to shower at home, rinse briefly at the beach to get the salt off and then dry once.
Do not wash your face in the morning and again before going out.
None of these is difficult. All of them reduce the count.
And the opposite problem
For completeness, the two extremes have their own failure modes.
Continuously wet skin, held wet for hours, softens progressively and becomes fragile and prone to maceration, which is why skin under a wetsuit for a long session is a specific case covered in the article on occlusion.
Continuously dry skin, without transitions, stiffens and cracks but does not suffer the bond fatigue described here.
The cycling case combines the vulnerability of the first with the mechanical stiffness of the second, which is why it is the worst of the three and why it is the ordinary condition of anyone who works or plays in water in Britain in winter.