Slugging guide: petrolatum occlusion for barrier repair and overnight hydration

Slugging — applying a thin layer of petrolatum (Vaseline) as the final step in a PM skincare routine — is one of the most evidence-supported barrier-repair techniques in skincare, with a well-understood mechanism and a strong safety profile. Here is the complete guide.

What slugging is

The technique

Slugging refers to applying white petrolatum or a petrolatum-based product (Vaseline, Aquaphor, CeraVe Healing Ointment) as the last step in the evening routine, after all serums and moisturizers have been applied. The term comes from the skin's appearance after application — shiny, like a slug's trail.

The product is applied thinly — a film, not a thick coating — over the face and allowed to remain overnight. It is rinsed off in the morning.

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Mechanism: occlusion and TEWL physics

Why petrolatum reduces water loss

The skin loses water continuously through the epidermis by passive diffusion — transepidermal water loss (TEWL). In healthy skin, the stratum corneum's lipid matrix (ceramides, cholesterol, fatty acids) naturally limits this loss. In compromised skin — dry skin, eczema, over-exfoliated skin, retinoid-disrupted skin — this lipid barrier is incomplete and TEWL increases.

Petrolatum's mechanism:
Petrolatum (a mixture of semi-solid hydrocarbons derived from petroleum) is hydrophobic — it does not dissolve in water
Applied to skin, it forms a continuous hydrophobic film across the surface
This film acts as a vapor barrier — water molecules diffusing upward from the epidermis cannot cross the hydrophobic film
TEWL reduction: 98% with an adequate petrolatum film — the most effective occlusive of any skincare ingredient

This is pure physical occlusion — petrolatum does not penetrate the skin, does not moisturize the skin (it contains no water), and does not provide humectant function. It simply prevents water that is already in the skin from escaping.

Why this matters for barrier repair

The skin's barrier lipids (ceramides, fatty acids) are synthesized in the stratum granulosum and secreted into the stratum corneum. This process requires normal transepidermal water activity — when the skin is severely dehydrated (high TEWL), synthesis is impaired. Occlusion restores the water activity needed for lamellar body lipid secretion and barrier reconstruction.

*Rawlings AV, Corcuff P, Agache P, Prunieras M. (1994). The effect of occlusion on stratum corneum lipid composition. Acta Dermato-Venereologica, 74(2), 88–92.* Demonstrated that occlusion accelerates stratum corneum lipid (ceramide) replenishment after experimental barrier disruption — the biophysical basis for using petrolatum in eczema and dry skin management.

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Why petrolatum is non-comedogenic

The comedogenicity myth

Petrolatum is oil-based and derived from petroleum — both facts lead many people to assume it will cause breakouts. The evidence consistently shows otherwise:

Petrolatum does not penetrate the follicular canal: Its large hydrophobic hydrocarbon chains cannot dissolve into the sebum-filled follicle. It remains as a surface film — it does not occlude pores in the way that small lipophilic molecules do.

Comedogenicity testing: Petrolatum consistently scores 0 (non-comedogenic) on the rabbit ear assay and is rated non-comedogenic in human studies. It is used in prescription wound care and post-procedure protocols specifically because it does not interfere with follicular healing.

The practical confirmation: Dermatologists have used petrolatum on post-procedure skin (after laser, peels, microneedling) for decades without comedone induction. Its occlusive film is on the surface, not in the follicle.

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Who benefits from slugging

Ideal candidates

Dry skin: Chronic dry skin with high baseline TEWL — slugging dramatically reduces overnight water loss and allows the skin to wake up with visibly improved plumpness and smoothness.

Eczema and atopic dermatitis: Petrolatum is a first-line recommendation in atopic dermatitis guidelines. It replaces the deficient barrier lipid function and reduces itch-scratch cycles that perpetuate barrier damage.

Retinoid users: During the retinization period, retinoids transiently impair barrier function. Slugging over retinoid (after the retinoid has absorbed — 20–30 minutes) reduces TEWL and mitigates dryness and peeling.

Over-exfoliated skin: AHA/BHA overuse causing sensitivity, tightness, and redness benefits from a slugging "reset" — 3–7 nights of slugging only (no actives) to allow barrier recovery.

Post-procedure: After laser, chemical peel, or microneedling, the epidermis is temporarily disrupted. Petrolatum-based occlusion is standard clinical practice for post-procedure care.

Cold/dry climates: Low-humidity environments increase TEWL — slugging provides the occlusion that compensates for the environment's drying effect.

Who should skip slugging

Oily and acne-prone skin: While petrolatum is non-comedogenic, the occlusive surface layer can trap heat and create a warm, humid microenvironment on the skin surface — potentially worsening inflammatory acne for some individuals. The evidence for petrolatum causing acne is absent, but the practical experience of some oily-skin patients is negative. Try on a small area first.

*Fungal acne (Malassezia folliculitis): An occlusive layer may worsen Malassezia* by creating the warm, humid environment it thrives in. Avoid slugging if fungal acne is active.

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How to slug correctly

The protocol

Complete your full PM routine: cleanser → toner (if used) → serums → moisturizer
Allow the moisturizer to absorb — 2–5 minutes
Apply a thin film of petrolatum over the face with clean fingers (pea-to-dime sized amount for the whole face — it spreads thin)
Sleep on a pillowcase you don't mind getting slightly greasy; or use a satin pillowcase
Morning: rinse face with lukewarm water (no cleanser needed unless the film feels heavy)

Over retinoid specifically: After retinoid application, wait 20–30 minutes for absorption, then slug. Do not apply petrolatum before the retinoid — it will prevent absorption.

Frequency

Dry/eczema skin: Nightly or most nights
Retinoid users: On retinoid nights (and recovery nights if very dry)
Normal skin maintenance: 2–3× per week; more frequently in winter or dry climates

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Petrolatum alternatives (other occlusives)

| Occlusive | TEWL Reduction | Notes |
|---|---|---|
| White petrolatum (Vaseline) | ~98% | Gold standard; cheapest |
| Aquaphor Healing Ointment | ~85% | Petrolatum + lanolin + glycerin; slightly more moisturizing |
| CeraVe Healing Ointment | ~95% | Petrolatum + ceramides; combination barrier support |
| Squalane | ~50% | Lighter; non-comedogenic; less effective occlusion |
| Shea butter | ~40% | Moderate occlusion; contains oleic acid (comedogenic for some) |

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