Petrolatum is a semi-solid mixture of hydrocarbons derived from petroleum that works primarily by slowing moisture loss from your skin. But it does more than simply sit on top like a plastic wrap. Research shows petrolatum actually permeates into the outer layer of skin, weaving between cells to reinforce the skin’s own protective structure while keeping water locked in.
How Petrolatum Works on Skin
Your skin’s outermost layer, called the stratum corneum, is built like a brick wall: tough skin cells held together by thin sheets of natural fats. When that lipid “mortar” gets damaged from dry air, harsh cleansers, or skin conditions, water escapes faster than normal and irritants get in more easily.
Petrolatum doesn’t just coat the surface. A study published in the Journal of Investigative Dermatology found that petrolatum permeates into the spaces between skin cells at every level of the stratum corneum, replacing damaged lipid layers. This means it acts as a temporary stand-in for your skin’s own fats, allowing normal barrier repair to continue underneath. It’s a surprisingly active role for what most people think of as a simple grease.
Petrolatum is made up of saturated hydrocarbons, typically with carbon chains longer than 25 atoms. Those large molecules don’t readily penetrate past the outermost skin layer into deeper tissue or the bloodstream. They stay where you need them: in the barrier itself.
Moisturizing and Eczema Management
Petrolatum is one of the most effective occlusive moisturizers available, meaning it forms a thin hydrophobic film that slows transepidermal water loss. For people with eczema (atopic dermatitis), regular use of emollients containing petrolatum is considered a cornerstone of treatment alongside prescription topicals. Clinical guidelines note that petrolatum, paraffin, and glycerin are the core ingredients in most moisturizers on the market, regardless of price point.
Comparative studies have generally found no strong evidence that one moisturizer outperforms another for eczema. The key variable is consistent use. One notable exception: aqueous cream, once widely recommended, has fallen out of favor because it contains sodium lauryl sulfate, which can increase skin irritation and inflammatory enzyme activity. It’s no longer recommended as a leave-on moisturizer for eczema patients. Plain petrolatum-based products avoid that problem entirely.
Wound Healing Without Antibiotics
If you’ve ever been told to apply antibiotic ointment to a minor wound, petrolatum may work just as well. A double-blind study in the Journal of the American Academy of Dermatology compared a petrolatum-based ointment to a combination antibiotic ointment on surgical wounds. At every checkpoint (days 7, 14, and 28), the two groups showed no differences in redness, swelling, scabbing, or skin regrowth. The antibiotic group actually reported more burning at the one-week mark, and one patient developed allergic contact dermatitis from the antibiotic product.
This matters because antibiotic ointments containing bacitracin or neomycin are among the most common causes of allergic skin reactions. Petrolatum keeps the wound moist, which is what promotes healing, without the risk of antibiotic allergy. Many dermatologists now recommend plain petrolatum for post-procedure wound care for exactly this reason.
Does Petrolatum Clog Pores?
Despite its heavy, greasy texture, petrolatum consistently scores as non-comedogenic in testing. In rabbit ear model studies, which are the standard method for evaluating whether an ingredient clogs pores, petrolatum did not cause comedones. That puts it in a different category from ingredients like isopropyl myristate or butyl stearate, which are proven pore-cloggers.
That said, non-comedogenic on a lab scale doesn’t mean it works well for every skin type. If your skin already produces plenty of oil, layering petrolatum on top adds lipid your skin doesn’t need and can make breakouts more likely in practice. The distinction is between petrolatum chemically blocking pores (it doesn’t) and petrolatum creating an environment where existing oil and bacteria get trapped (it can, on the wrong skin type).
Slugging: When It Helps and When to Skip It
The skincare trend called “slugging,” where you apply a thick layer of petrolatum as the final step in your nighttime routine, is essentially a maximalist version of occlusive moisturizing. For people with dry, dehydrated, or compromised skin barriers, it can deliver noticeable improvement overnight by preventing moisture loss while you sleep.
Cleveland Clinic dermatologists recommend skipping slugging if you have oily skin, acne-prone skin, or any active skin infection. You should also avoid layering petrolatum over products containing alpha hydroxy acids, beta hydroxy acids, or retinoids. Those active ingredients can cause irritation on their own, and trapping them under an occlusive seal intensifies the effect. If you want to slug, keep the layers underneath simple: a gentle cleanser, a basic hydrating serum or moisturizer, then the petrolatum on top.
Safety and Purity Standards
One concern that comes up frequently is whether petrolatum contains harmful contaminants, specifically polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic compounds found in crude petroleum. The answer depends entirely on how the product is refined. Industrial-grade petrolatum can contain PAH impurities. Cosmetic and pharmaceutical-grade petrolatum sold in the U.S. is a different product.
The United States Pharmacopeia (USP) sets specific purity standards for petrolatum used in drugs and skincare. These standards include a dedicated UV absorbance test designed to detect polycyclic aromatic hydrocarbons. Products labeled “USP petrolatum” or “white petrolatum” have passed this screening. The concern about contamination applies to unrefined or industrial petroleum jelly, not to the refined versions found in drugstore skincare products from established brands.