Occlusives form a protective and impenetrable layer on the surface of your skin to create a barrier that prevents moisture loss. Occlusion means covering skin with occlusives, like impermeable dressings, tapes, gloves, transdermal devices or petrolatum, which decreases the water gradient across the stratum corneum.
A Double Edged Sword
Proceed cautiously with occlusion. On one end, it can seal in hydration to prevent dryness and flakiness. On the other, it can act as a penetration enhancer and induce maceration. Watch out for what you are occluding; any irritating ingredient can become more irritating as occlusion may allow it to penetrate further, causing more irritation. Examples of these are barrier looseners like AHA and some forms of low molecular Hyaluronic Acid.
In contrast to this, occlusion may prevent the penetration of other actives. Some authors argue that there are actives that are affected by the skin's water gradient. Occlusion decreases this gradient, which explains why certain actives penetrate less. It's a very unpredictable phenomenon, and we can't generalize which ones would lead to less penetration and which ones would lead to more.
How Occlusion Hydrates
Slugging is a term used when people slather Petroleum Jelly on their face over top of their routine. The term originated in Korea as snail mucin was becoming more common in skincare. Snail, slug, same, same. Slugging prevents the escape of hydration, like in the case of Tretinoin usage.
The use of petrolatum alone, however, may do more harm than good. It was recently proven that it can delay barrier repair when used alone than when just letting the skin repair itself. Upon examination by electron microscope, it was seen that it forms an impenetrable barrier that repair enzymes cannot access.
Although petrolatum has these disadvantages, it is still the unbeatable gold standard in decreasing water loss. Applying it over-hydrating serums like Wave serum and the barrier lipids in C.R.E.A.M. would be guaranteed to hydrate your skin effectively.
How much Occlusion is too much?
The goal for using a moisturizer is to prevent moisture loss (TEWL). Most moisturizers can decrease TEWL by 30-40%; below 30% isn't enough to hydrate the skin. If the TEWL value is decreased by more than 40%, then there's the chance for maceration to happen. Maceration occurs when skin is in contact with moisture for too long. Macerated skin looks lighter, wrinkly and is more susceptible to breaks and tears. This is what happens in the case of diaper dermatitis. Baby's butt is occluded by the diaper, and the area is always moist, which makes it extra fragile and more prone to bacterial growth. When you occlude your skin too much (e.g. using sheet masks often), try to be careful with the products your apply afterwards. It's a good idea to close your barrier with a moisturizer right after wearing a hydrating face mask.
How much Petrolatum should be applied to get the optimum 30-40% decrease in TEWL?
It was shown that applying more than 6 grams (1.2 tsp) of petrolatum on the face leads to increased hydration of the skin, but is accompanied by marked swelling of the corneocytes. This can also lead to the increased penetration of whatever active was applied before the petrolatum. A thin layer should do the job without risking overhydration.
Occlusion isn’t for everyone, but if it’s for you, it can do wonders for dehydrated skin. Remember to always keep your skincare priority top of mind and use these following tips to optimize occlusion:
- Barrier Repair: occlude C.R.E.A.M. or another well-formulated ceramide moisturizer. You can also try occluding some barrier humectants like Panthenol, High molecular weight Hyaluronic Acid, and Glycerin. If you're focused on hydration, make sure the barrier is repaired, and then add in hydrating serums that include Urea, Lactic acid, etc.
- Inflammation and Acne: Try to avoid immediately occluding irritating actives like Benzoyl Peroxide, Salicylic acid, Retinoids etc. Wait for an hour or so before occluding these as occlusion serves as a penetration enhancer. Occlusion might not be suited for acne-prone people, but it depends on the cause of acne.
- Pigmentation: avoid immediately occluding harsh actives like AHAs and Retinoids.
- Texture: occlude all the way, but don't exceed more than 6 grams of occlusion for the whole face. Also, don’t forget your neck ;)