What occlusion actually means
Occlusion is simply the state of being covered by something that stops water evaporating from the surface.
It is used deliberately in skin care, because holding water in the outer layer is exactly what an occlusive layer does and it is genuinely useful for short periods. It is also a load, because a layer held fully hydrated for hours behaves differently from one at normal water content.
A wetsuit is occlusion at scale: most of the body, for one to four hours, at a raised temperature, with a wet film against the skin throughout.
The layer softens progressively
Held at full hydration, the corneocytes stay swollen, the lipid sheets stay stretched and the connections between cells stay strained. Over hours, the layer becomes progressively softer and more fragile.
Softened skin is easy to remove mechanically. That is the reason so many wetsuit rashes are on skin that has been under a moving seam, and it is also the reason that peeling a suit off at the end is a higher risk moment than putting it on at the start.
At the extreme, skin held wet long enough becomes macerated: pale, wrinkled, soft and easily broken. It is most obvious in the places that stay wettest and least ventilated, and it recovers over hours once the skin is dry and left alone.
The warmth changes the chemistry too
A wetsuit works by limiting water exchange and by insulating, so the film against your skin warms up.
Three things follow. You sweat into it, so the film is not just sea water. Warmth increases the mobility of skin lipids, so more is lost to the film than would be at sea temperature. And a warm, wet, enclosed environment is a different microbiological environment from cold open skin, which matters for how kit smells and for how skin under it behaves.
We are going to be careful about the last point rather than dramatic. What can be said is that warm wet enclosed skin is a recognised setting for skin problems, that broken skin in that setting is an entry point, and that anything that looks like an infection, meaning increasing redness, heat, swelling, pain, pus or fever, is a same day medical matter and not a subject for a website.
Seams, panels and the mechanical layer
The rashes people actually get are usually mechanical rather than chemical, and they occur where a hard or thick element moves repeatedly over softened skin.
The classic sites are the neck under a collar, the underarm where a panel folds, the backs of the knees, the front of the ankles where boots meet, the wrists at seals, and the sternum under a zip or a chest seam. All of them are places where movement is unavoidable and where a seam is thicker than the material around it.
The mechanism is friction against a softened layer, and the controls are the ones you would apply to any friction problem: reduce the relative movement, reduce the coefficient of friction at the contact, or interpose something. That is covered properly in the article on friction and chafe.
The specific point for occlusion is that the same seam that does nothing on dry skin will cause a problem on skin that has been held wet for two hours, so the tolerance in summer tells you nothing about the tolerance in a long winter session.
| Site | Why there | The control that fits the mechanism |
|---|---|---|
| Neck under the collar | Constant head movement against a thick edge on softened skin | Reduce relative movement, interpose a smooth layer |
| Underarm | A panel that folds and moves through the whole session | Fit, and a smooth interface at the fold |
| Backs of the knees | Repeated flexion, thick seam, poor ventilation | Fit, and rinsing and drying the suit between uses |
| Front of the ankles | Boot top meets suit leg, both moving | Overlap direction, and a smooth interface |
| Wrists at the seals | A tight seal on skin that is also washed constantly | Seal fit, and drying properly afterwards |
| Under a hood | The worst ventilated item, held against scalp and forehead | Rinse and dry the hood, and rinse the scalp |
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.
The hygiene point that people skip
A wetsuit is a garment that is worn against the skin, gets warm, gets wet with body fluids and is then frequently left in a bag.
Rinsing kit after use, and drying it properly, is a skin control and not merely a kit longevity control. A suit that is rinsed and dried presents a cleaner surface to softened skin next time. A suit that is put away damp does not.
The same applies to boots, gloves and hoods, which are smaller, worse ventilated and closer to the skin sites that cause most trouble. If one item of your kit is responsible for most of your skin complaints, it is very often the hood or the boots.
Coming out of occlusion
The moments after removing a wetsuit are the most consequential of the session for the skin, and they are the ones done in a hurry in a car park while cold.
Peel rather than drag, because the layer underneath is softened. Rinse the salt off, because it is a drawing agent and an abrasive. Blot rather than rub. Get dry and warm reasonably quickly, because a softened cold layer in wind is being loaded from three directions. Then apply something, while the skin is still slightly damp.
The realistic version of all of that, done properly, in cold weather, in a car park, is set out in the car park routine, which is the article people actually need.