What does petroleum jelly actually do to the skin?
Petrolatum forms a physical seal that blocks water evaporation (TEWL (transepidermal water loss)) the process that happens anyway in normal skin but accelerates dramatically when your barrier is compromised. This isn't a mystery mechanism.
It doesn't add moisture; it traps what's already there, which means the hydrating products underneath matter enormously. That's why you apply it over serums and moisturisers, never on dry skin. This straightforward mechanism has been studied since the 1970s.
A 2016 study published in the Journal of Investigative Dermatology found that petrolatum, when applied to disrupted skin barrier, not only reduced water loss but also upregulated the expression of filaggrin: a key structural protein in skin barrier function. This suggests it may support barrier repair at a molecular level, not merely seal the surface. Research in eczema populations consistently shows petrolatum-based emollients reduce flare frequency and symptom severity.
Who benefits most from slugging?
Dry and eczema-prone skin benefit most: their barrier is actively leaking water, and petrolatum stops it dead. It's brilliant during repair from over-exfoliation, active reactions, or winter weather when your barrier needs maximum support.
Sensitive skin thrives on petrolatum because it's basically one ingredient: minimal ingredients mean minimal chance of triggering a reaction. Dermatologists recommend it post-treatment (after peels and lasers) specifically because it won't interfere with healing.
Acne-prone and oily skin types may find that heavy occlusion overnight traps sebum and existing comedones, worsening congestion. Even though petrolatum itself doesn't cause new comedones. A lighter approach (such as a non-occlusive barrier cream rather than petrolatum) may be preferable. If you have fungal acne (Malassezia folliculitis), avoid petrolatum. It can feed the yeast responsible.
Does the order of products matter?
Yes. Applied early or mid-routine, petrolatum seals out everything after it. Always apply last, after all serums and moisturisers, so it locks in everything beneath it.
Use a thin layer massaged until barely visible. You don't need an opaque coating, and less is more comfortable to sleep in.
What to think about before you try it
- Check whether your skin is dry or dehydrated: petrolatum helps both, but dehydration also responds well to humectant-only products and doesn't always need slugging.
- If you use retinoids, be aware that occlusion can increase active penetration: which may cause irritation. A short application window before slugging, or avoiding slugging on retinoid nights, reduces this risk.
- If you have persistent breakouts or congestion, try a patch test for 1–2 weeks on your jawline before committing to full-face slugging.
- Look for cosmetic-grade (highly refined) petrolatum: the refinement process removes potential irritants present in unrefined versions.
When to see a dermatologist
If you have chronic skin barrier issues. Persistent redness, eczema, or significant dryness that doesn't improve with barrier support: a dermatologist can identify whether there is an underlying condition (atopic dermatitis, contact dermatitis, rosacea) that requires targeted treatment rather than topical management alone. Slugging is a helpful support tool, not a treatment for diagnosable skin conditions.
References
- Danby SG, AlEnezi T, Sultan A, et al. Effect of olive and sunflower seed oil on the adult skin barrier: implications for neonatal skin care. Pediatr Dermatol. 2013;30(1):42-50. PubMed
- Czarnowicki T, Malajian D, Khattri S, et al. Petrolatum: Barrier repair and antimicrobial responses underlying this "inert" moisturizer. J Allergy Clin Immunol. 2016;137(4):1091-1102. PubMed
- Lodén M. Role of topical emollients and moisturizers in the treatment of dry skin barrier disorders. Am J Clin Dermatol. 2003;4(11):771-788. PubMed