Slugging: Science or Hype? What the Evidence Says | Boldpurity

What Is Slugging in Skincare?

Slugging is an overnight skincare technique in which a thin layer of an occlusive product, most commonly petrolatum (petroleum jelly), is applied as the final step of an evening skincare routine. The term "slugging" is relatively new in popular skincare discourse, but the practice is based on an established dermatological principle: occlusion.

The goal of slugging is to create a protective occlusive layer that reduces water loss from the skin surface overnight, helping to maintain and increase surface hydration.

Historical Context

Petrolatum has been used in skincare and dermatology for over a century. Healthcare professionals have long recommended occlusives to support skin barrier health and reduce water loss. Slugging is essentially the application of this established dermatological principle as a social-media skincare trend.

Common Slugging Products

Petrolatum is the most common slugging product; however, other occlusives can be used, including:

• Petrolatum (petroleum jelly)
• Lanolin (wool wax)
• Mineral oils
• Thick occlusive creams or balms
• Some heavier moisturizers with high occlusive content

For this article, focus is on petrolatum, the most widely used and studied slugging product.

How Occlusion Works: The Science

Slugging is based on the principle of occlusion, a well-established concept in dermatology. Understanding occlusion helps explain how petrolatum affects the skin.

What Is Occlusion?

Occlusion refers to creating a physical barrier on the skin surface that reduces the movement of water and other substances across the skin barrier. An occlusive layer sits on top of the skin and restricts the evaporation of water from the skin surface into the air.

The Skin Barrier and Water Loss

Healthy skin naturally loses water through a process called transepidermal water loss (TEWL). This is a normal physiological process—the skin is not completely waterproof. The stratum corneum (the outermost layer of skin) acts as a semi-permeable barrier, allowing some water vapor to escape.

Dry skin, cold weather, harsh cleansing, or compromised skin barriers increase TEWL. By reducing water loss through occlusion, slugging can help maintain surface hydration.

How Petrolatum Works as an Occlusive

Key point: Petrolatum works by reducing water loss, not by adding hydration or nourishment to the skin. This distinction is important.

Slugging and Transepidermal Water Loss (TEWL)

Transepidermal water loss (TEWL) is the amount of water that evaporates from the skin surface to the air. It is a normal physiological process, but elevated TEWL is associated with dry skin, skin barrier compromise, and skin sensitivity.

Normal TEWL

Healthy skin loses approximately 0.5–10 grams of water per square meter of skin per hour, depending on humidity, temperature, and individual variation. This baseline loss is normal and necessary.

What Slugging Can Do

Research on occlusive materials, including petrolatum, shows that they can reduce TEWL by 50–99%, depending on the occlusive material and measurement conditions. This reduction is temporary and lasts only as long as the occlusive barrier remains intact.

Practical meaning: Slugging may reduce water loss overnight, leading to visibly more hydrated, plumper skin in the morning. However, the effect resets when you wash your face.

What Slugging Cannot Do

Slugging does not:

• Permanently reduce TEWL
• Repair a damaged skin barrier (permanent repair requires time and supportive skincare)
• Add hydration to the skin (occlusives reduce loss, but don't hydrate)
• Treat dehydration or skin conditions (these require appropriate medical or cosmetic interventions)

What Petrolatum Actually Does

Petrolatum (petroleum jelly) is one of the most studied and widely used occlusives in skincare and dermatology. Understanding what it does—and what it doesn't—is important for realistic expectations.

Petrolatum as an Occlusive

• Reduces TEWL: Multiple studies confirm that petrolatum reduces transepidermal water loss significantly
• Increases surface moisture: By preventing evaporation, petrolatum increases moisture content at the skin surface
• Improves skin appearance temporarily: Higher surface moisture can lead to smoother, plumper-looking skin overnight
• Non-penetrating: Petrolatum does not significantly penetrate the skin; it works on the surface
• Non-comedogenic: Petrolatum itself does not inherently clog pores; however, in oily or acne-prone skin, applying an occlusive may trap bacteria or sebum

Petrolatum Does Not Provide

• Hydration: Petrolatum does not add water to the skin; it only reduces loss
• Nourishment: It does not contain vitamins, minerals, or skin-conditioning ingredients
• Active benefits: Unlike serums with active ingredients, petrolatum has no enzymes, actives, or functional ingredients
• Humectant effects: Unlike glycerin or hyaluronic acid, petrolatum does not draw water into the skin
• Permanent changes: All benefits are temporary and reset when the occlusive is removed

Why This Matters

Slugging is best understood as a temporary surface hydration technique, not a treatment or repair. It may feel nice and look effective overnight, but it does not change the skin's fundamental biology or barrier function over time.

Slugging vs. Moisturizer

A common misconception is that slugging and moisturizers serve the same function. They do not. Understanding the difference helps clarify when each might be appropriate.

Bottom line: Slugging is an occlusive only. A complete moisturizer provides hydration, nourishment, and occlusion. They are not interchangeable.

Slugging for Different Skin Types

Slugging works differently depending on skin type. What is beneficial for dry skin may be uncomfortable or counterproductive for oily or acne-prone skin.

Slugging for Dry Skin

Dry skin benefits most from occlusion because it typically has elevated TEWL and moisture loss. Slugging can help dry skin feel more comfortable and appear smoother overnight.

• Benefit: Reduces water loss; skin appears more hydrated
• Frequency: Can be used nightly if desired
• Tip: Layer slugging over a hydrating moisturizer for best results

Slugging for Oily Skin

Oily skin typically has normal or low TEWL and does not benefit from additional occlusion. Slugging may feel uncomfortable, heavy, or greasy for oily skin types.

• Consideration: May feel uncomfortable or contribute to congestion
• If interested: Try less frequently (1–2 times weekly) or use on dry areas only
• Alternative: Skip slugging; use a lightweight moisturizer instead

Slugging for Acne-Prone Skin

The effect of occlusion on acne-prone skin varies. For some individuals, an occlusive layer may trap bacteria or sebum, worsening breakouts. For others, occlusion may feel fine.

• Concern: May potentially exacerbate breakouts by trapping bacteria/sebum
• Patch test: If interested, test on a small area first
• Frequency: If using, limit to 1–2 times weekly initially
• Professional guidance: Ask a dermatologist if unsure whether slugging is appropriate

Slugging for Sensitive Skin

Sensitive skin can be either dry or normal. The appropriateness of slugging depends on the underlying cause of sensitivity.

• If sensitive and dry: Slugging may provide comfort
• If sensitive and reactive: The heavy occlusion may feel uncomfortable; lighter alternatives may be better
• Test carefully: Introduce slowly; watch for irritation or discomfort

Individual response matters. Slugging is not universally appropriate; personal tolerance is the guide.

Slugging With Active Ingredients

A common question: Can you slug over retinol, acids, vitamin C, or other active ingredients? The answer is nuanced and depends on the specific active and individual tolerance.

General Principle

Occluding strong active ingredients can increase their concentration on the skin surface and potentially increase irritation, sensitivity, or adverse effects. Many dermatologists recommend avoiding occlusion over active ingredients, particularly during the introduction phase.

Slugging Over Retinoids

• Recommendation: Do not occlude retinoids initially; retinoids are best used with barrier-supporting moisturizers, not heavy occlusives
• Why: Retinoids increase skin sensitivity and irritation; occlusion may increase these effects
• Alternative: Use a lightweight moisturizer after retinoid, not a heavy occlusive

Slugging Over Acids (AHAs/BHAs)

• Recommendation: Do not occlude chemical exfoliants; they may cause excessive irritation when occluded
• Why: Acids work by exfoliating the skin surface; occlusion traps them and may increase irritation
• Alternative: Use on separate nights from slugging, if desired

Slugging Over Vitamin C

• Recommendation: Light occlusives may be acceptable; heavy occlusion is not ideal
• Why: Vitamin C is less irritating than retinoids or acids; however, occluding may still increase irritation
• Alternative: Use vitamin C in the morning; slug at night only

Best practice: Keep slugging separate from active ingredients, particularly when first introducing them. Use slugging on non-active nights, or pair it only with gentle moisturizers and supportive products.

Climate Considerations

The appropriateness of slugging varies significantly with climate and humidity.

Slugging in Dry Climates

Dry climates favor slugging. Low humidity increases TEWL, making occlusion more beneficial.

• Benefit: Maximum reduction in water loss
• Frequency: Can be used frequently, even nightly
• Comfort: Generally comfortable year-round

Slugging in Humid Climates

High humidity reduces TEWL naturally; the skin already retains moisture well. Slugging may feel unnecessary or uncomfortable.

• Consideration: Heavy, greasy feel may be uncomfortable
• Frequency: May want to use less frequently or skip entirely
• Risk: Occlusion in high humidity may trap sweat or bacteria, potentially worsening breakouts

Seasonal Variation

Climate changes seasonally. Slugging frequency can adjust accordingly:

• Winter (dry): More frequent slugging may be beneficial
• Summer (humid): Less frequent or no slugging
• Spring/Fall: Variable; based on local humidity

Practical approach: Adjust slugging frequency based on how your skin feels and your local climate. There is no universal "right" frequency.

How Often Should You Slug?

There is no universal frequency that works for everyone. Frequency depends on skin type, climate, personal tolerance, and results.

General Starting Points

• Dry skin: 2–7 times weekly (or nightly if desired)
• Combination/normal skin: 2–3 times weekly
• Oily skin: 1–2 times weekly (or skip entirely)
• Acne-prone skin: 1 time weekly or less (patch test first)

How to Determine Your Frequency

Start conservatively and adjust based on how your skin responds:

1. Begin with 2 times weekly
2. Observe skin for 2–3 weeks
3. If comfortable and beneficial, maintain or increase slightly
4. If uncomfortable, reduce frequency or discontinue

Signs You May Be Slugging Too Often

• Breakouts or congestion
• Increased greasy appearance
• Discomfort or itching
• Worsening skin condition (for acne-prone skin)

If these occur, reduce frequency or take a break from slugging.

Illustrative Hypothetical Scenarios

Important note: The following scenarios are illustrative hypothetical examples for educational purposes only. They are not clinical cases, and outcomes are not guaranteed or typical for everyone. Individual results vary significantly.

Scenario 1: Maya — Dry Skin in Winter

Background: Maya, 32, has naturally dry skin. In winter, her skin becomes very tight and flaky.

Approach: During winter months, Maya uses a hydrating moisturizer followed by petrolatum slugging 4–5 nights weekly.

Hypothetical outcome (illustrative only): Skin feels more comfortable overnight; less flaking in the morning. By week 2, she notices reduced tightness and improved appearance.

Why this works: Dry skin benefits from occlusion; winter climate favors slugging. Combining moisturizer + occlusive addresses both hydration and water loss.

Scenario 2: Jamal — Oily Skin and Slugging

Background: Jamal, 28, has oily, acne-prone skin. He is curious about slugging but concerned about breakouts.

Approach: Jamal decides to test slugging on a small area (forehead only) once weekly, starting with a very thin layer.

Hypothetical outcome (illustrative only): Week 1: No negative reaction; skin feels hydrated. Week 2–3: Mild breakout on the slugged area. Jamal stops slugging and returns to his regular routine.

Why this matters: Slugging is not appropriate for all individuals; personal tolerance is the guide. Testing first prevented a larger problem.

Scenario 3: Priya — Slugging With Retinol

Background: Priya, 35, uses a retinol serum at night. She wants to add slugging for extra hydration.

Approach: Initially, Priya applies retinol, then a lightweight moisturizer, and then petrolatum. Within days, she experiences increased irritation and redness.

Hypothetical outcome (illustrative only): Priya discontinues the occlusive and reverts to retinol + lightweight moisturizer only. Irritation resolves within 1 week. She reserves slugging for non-retinol nights.

Why this matters: Occluding active ingredients can increase irritation. Separating them often works better.

Common Slugging Myths

Frequently Asked Questions