Slugging became one of the most discussed skincare trends in recent years, particularly on Reddit skincare communities and TikTok. The concept is simple: apply an occlusive product, usually petroleum jelly (Vaseline), as the final step of your evening skincare routine and leave it on overnight. The name comes from the slightly shiny, “slug-like” appearance it creates. The results are genuinely impressive for some skin types and genuinely problematic for others.
The science behind occlusion
Transepidermal water loss (TEWL) is the continuous evaporation of water through the skin surface. A healthy, intact skin barrier limits this, but various factors increase it: dry weather, central heating, ageing, certain skincare ingredients, and barrier conditions like eczema.
Occlusive ingredients create a physical barrier on the skin surface that slows or stops TEWL. Petrolatum (petroleum jelly) is one of the most effective occlusives known, with a reduction in TEWL of up to 98% in some measurements. It does not add moisture to the skin, it traps existing moisture already present.
This is why slugging is most effective when done after a hydrating routine. Apply humectants like hyaluronic acid and water-based serums first. Then apply your moisturiser. The petroleum jelly goes on last to seal everything in rather than just sitting on top of dry skin.
Overnight is the optimal time because the skin barrier goes into repair mode during sleep. Cells turn over and repair more actively between approximately 11pm and midnight, and the barrier recovers from daytime exposure. Locking in moisture during this repair window enhances the process.
Who benefits from slugging
Dry, very dry, and eczema-prone skin is where slugging has the most compelling case. People with compromised skin barriers who wake up with tight, flaky, or reactive skin can see significant improvements in hydration, redness reduction, and overall barrier health within a few days of consistent slugging.
Skin recovering from over-exfoliation, retinoid adjustment periods (the initial weeks of starting a retinol or tretinoin routine when skin becomes dry and reactive), or after procedures like laser or chemical peels benefits from enhanced occlusion to support healing.
Cold, dry climates where indoor heating drops humidity dramatically create conditions where external occlusion helps. People in Estonian winters, with heating systems running continuously, may find their skin genuinely benefits from this extra layer of protection overnight.
Mature skin that produces less sebum and has a naturally drier barrier tends to respond well. The decreased natural occlusion from reduced lipid production is partly compensated by the external layer.
Who should avoid it
Oily and acne-prone skin is the most commonly cited reason to avoid slugging. Petroleum jelly has a comedogenic rating that is debated (some sources rate it very low, others moderately higher), but the practical experience is that completely occluding oily skin overnight can contribute to clogged pores and breakouts in people who are already prone to them. The trapped environment under the petroleum layer can also potentially trap bacteria along with moisture.
Fungal acne (malassezia folliculitis) is a specific concern. The yeasts responsible for fungal acne thrive in lipid-rich, warm, occluded environments. Petroleum jelly over fungal acne-prone skin creates ideal conditions for it to worsen.
Sensitive skin that reacts unpredictably to products should patch test first. Petroleum jelly itself has very low allergen potential, but applying it overnight over active serums and moisturisers increases penetration of those underlying products, which can trigger reactions in sensitive skin.
What to actually use for slugging
Pure petroleum jelly (petrolatum) is the most common and most studied option. It is non-comedogenic for most people, fragrance-free, and very inexpensive. Medical-grade petrolatum, sold under brands like Vaseline, is the same ingredient used in wound care and dermatology.
Some people prefer alternatives that feel less heavy. Squalane is a lighter occlusive that is better tolerated by oily and combination skin. It does not provide the same level of TEWL reduction as petrolatum but is less occlusive and more compatible with a wider range of skin types.
Lanolin (wool wax) is a powerful natural occlusive but has a significant allergen rate, particularly for people with wool or lanolin sensitivity, which makes it a higher-risk choice.
Shea butter sits somewhere between petrolatum and squalane in terms of occlusive strength. It is richer than squalane but less occlusive than petrolatum, and adds emollient and some nourishing fatty acid benefits. For people who want something effective but prefer to avoid petroleum-derived ingredients, a rich shea-based balm as the final step achieves a meaningful occlusive effect.
Practical tips for incorporating slugging
Start with two to three nights per week rather than every night. This allows you to assess your skin’s response without committing to daily occlusion before you know how your skin reacts.
A thin layer is sufficient. You do not need a thick mask of petroleum jelly; a thin application is enough to achieve the occlusive effect. A thick layer is uncomfortable, transfers to pillowcases heavily, and does not provide proportionally better results.
Switch to a silk or satin pillowcase if you slug regularly. Cotton absorbs the occlusive product and reduces its effectiveness, and the friction on skin that has been softened by overnight hydration is not ideal.
Be particularly careful not to get heavy occlusives too close to the eyelid skin, which is thinner and more prone to milia (small white keratin cysts) when blocked by heavy products.
The honest assessment
Slugging is a legitimate technique with good theoretical backing and practical results for appropriate skin types. It is not a cure or a complete skincare approach; it is one tool. For dry, damaged, or very sensitive skin seeking improved overnight hydration, it is worth trying. For oily, acne-prone, or fungal acne-prone skin, the risks outweigh the benefits for most people. The polarised opinions it generates online reflect genuinely different experiences from people with genuinely different skin types, and both camps are usually right about their own skin.