Slugging, the practice of applying a thin layer of a very occlusive product as the last step of a nighttime skincare routine, became widely discussed through skincare communities in recent years. The name refers to the shiny, slightly slimy appearance of the face after applying a thick occlusive (the comparison to a slug’s trail). Despite the unflattering name, the underlying principle is solid and based on well-established skin physiology.
What occlusion does
Transepidermal water loss (TEWL) is the continuous evaporation of water through the skin barrier. In healthy skin with an intact stratum corneum, TEWL is kept low by the lipid bilayer structure between skin cells. When the barrier is compromised, TEWL increases and skin becomes dry, reactive, and slower to repair.
An occlusive creates a physical film on the skin surface that dramatically reduces water evaporation. Unlike humectants (which draw water into the skin) or emollients (which fill the spaces between skin cells and improve suppleness), occlusives work by reducing the rate at which water leaves through the surface. Applied over products already on the skin, an occlusive traps everything underneath and extends the contact time of all the actives and humectants applied before it.
This is why slugging as a concept works: by applying a highly occlusive final layer, you maximise the overnight hydration of everything you applied before it. The skin wakes up plumper, smoother, and more hydrated than it would be after the same routine without the occlusive layer.
Petrolatum: the gold standard occlusive
Petrolatum (petroleum jelly, Vaseline) is the most commonly used slugging product because it has the highest occlusive efficiency of any ingredient studied in skin science. A classic 1972 study by Blank and Scheuplein established that petrolatum reduced TEWL by about 98%, more than any other material tested. It is also hypoallergenic, inert, and well-studied for safety.
The derivation from petroleum creates a discomfort for natural beauty consumers. Petrolatum is refined and purified, the cosmetic-grade material contains no aromatic hydrocarbons that would raise health concerns, but it is not a plant-derived ingredient. For natural skincare, plant-based occlusive alternatives provide meaningful but somewhat lower occlusive efficiency.
Natural occlusive alternatives
For those who prefer plant-based occlusives, several options approach the TEWL-reduction of petrolatum at practical concentrations:
Shea butter is the most effective plant-based occlusive in most formulations, combining its high stearic acid content with the additional anti-inflammatory activity of its triterpene fraction. Applied as the final step, a thin layer of shea butter provides substantial TEWL reduction overnight. Approximately 70-80% TEWL reduction compared to petrolatum’s 98% is achievable with a well-applied shea layer.
Beeswax (not vegan) provides very strong occlusion with additional emollient properties. It is used in many balm formulations as the primary occlusive.
Coconut oil provides moderate occlusion (lower than shea or petrolatum) and has the additional benefit of penetrating the hair shaft, but on the face, its high lauric acid content and relatively comedogenic nature makes it less suitable for acne-prone skin than shea.
Cocoa butter, mango butter, and kokum butter provide occlusion comparable to shea at similar concentrations. The specific butter choice can be made based on skin type and texture preference; the occlusive mechanism is the same.
Hyaluronic acid is often confused with an occlusive because it is associated with hydration. It is actually a humectant: it draws water to the skin but does not seal it in. Applying hyaluronic acid without an occlusive layer over it in dry conditions can actually increase TEWL by attracting moisture from deeper skin layers to the surface where it then evaporates.
Who benefits from slugging
Dry and very dry skin types benefit most directly. Slugging overnight consistently produces noticeably more hydrated, supple skin in the morning for dry skin types. The barrier repair effects of sustained overnight occlusion are also meaningful for eczema and chronically dry skin.
Compromised or sensitised skin benefits from the barrier-creating layer that reduces irritant penetration overnight. If your skin has been over-exfoliated, reacting to a new product, or is generally more sensitive than usual, a slugging night gives the barrier a chance to repair without environmental challenge.
Mature skin produces less sebum and has reduced barrier function, making it more prone to overnight dehydration. A final occlusive layer is more beneficial for 40+ skin than for oily skin that already has a more robust natural lipid barrier.
When to avoid slugging
Oily and acne-prone skin should be careful. An occlusive layer over actives traps everything, including comedogenic ingredients if any are in your routine. For very oily skin, the additional occlusion is often unnecessary and can contribute to congestion, particularly around the nose and chin where sebaceous gland density is highest.
Do not slug over retinoids, acids, or any active at a concentration that already risks over-penetration. Occluding highly active products drives more penetration, which is useful when intentional but potentially irritating if you are already at the upper limit of what your skin barrier can handle. On retinoid nights, either skip the occlusive or use a very small amount over your moisturiser only.
Slugging is best done a few nights a week rather than every night for most people, which allows the skin barrier natural movement overnight and prevents the face feeling overly sealed. The benefits are most significant for dry and compromised skin; normal skin can use it occasionally for intensive hydration without making it a nightly practice.