Petroleum jelly is a purified mixture of semi-solid hydrocarbons obtained from crude oil. More specifically, it’s composed of saturated hydrocarbons, mainly paraffinic in nature, meaning long chains of carbon and hydrogen atoms. These molecules are what give it that familiar slippery, waxy texture and its ability to form a moisture-trapping barrier on skin.
The Hydrocarbons Inside the Jar
At the molecular level, petroleum jelly is a blend of three types of hydrocarbons: mineral oils (liquid at room temperature), paraffin waxes (solid at room temperature), and microcrystalline waxes (also solid, but with smaller crystal structures). The semi-solid consistency you feel when you dip your finger in is the result of these liquid and solid components blended together naturally. The carbon chains in petroleum jelly are long, typically ranging from about 25 carbons per molecule on the short end to 50 or more on the long end. Shorter chains would make it too runny; longer chains would make it too stiff.
All of these molecules are “saturated,” which in chemistry means the carbon atoms are fully bonded to hydrogen atoms with no reactive double bonds. This is part of why petroleum jelly is so stable. It doesn’t react easily with air, water, or most chemicals, which is also why it has such a long shelf life.
From Crude Oil to Your Medicine Cabinet
Petroleum jelly starts as the heaviest fraction left over from crude oil refining, known as vacuum residue. This is the thick, dark material that remains after lighter products like gasoline, diesel, and lubricating oils have been distilled off. In its raw state, this residue contains impurities that need to be removed before the product is safe for skin or food contact.
The refining process involves several steps. First, a process called propane deasphalting separates the waxy, jelly-like material from the asphalt-like components. Then hydrogenation uses hydrogen gas under pressure to break down unstable compounds and remove sulfur, nitrogen, and other impurities. Solvent dewaxing adjusts the ratio of liquid to solid hydrocarbons to achieve the right consistency. Finally, filtration through adsorbent materials like activated carbon or bauxite (a clay mineral) removes remaining color bodies and contaminants.
Historically, manufacturers used “bone-black,” a porous charcoal made from animal bones, as a filtering material. Modern production has largely moved to synthetic adsorbents and activated carbon instead.
White vs. Yellow Petroleum Jelly
The difference between white and yellow petroleum jelly comes down to how thoroughly it’s been refined. Yellow petroleum jelly has undergone standard purification but retains some of its natural color from trace organic compounds. White petroleum jelly goes through additional decolorizing steps until it is “wholly or nearly decolorized,” according to the US Pharmacopeia standard. It must pass a strict color test: when melted, it can’t be darker than a very pale reference solution.
White petroleum jelly also has tighter limits on residual acidity, alkalinity, and leftover ash (no more than 0.05% residue when burned). Both grades are considered safe for skin use, but white petroleum jelly is the standard for pharmaceutical and cosmetic products. It may also contain a small amount of antioxidant to prevent the hydrocarbons from slowly degrading over time.
How Purity Is Regulated
The main safety concern with any petroleum-derived product is contamination by polycyclic aromatic hydrocarbons (PAHs), a family of compounds that can form during oil processing and are linked to health risks at high exposures. Fully refined, cosmetic-grade petroleum jelly contains extremely low levels of these contaminants. The FDA sets strict ultraviolet absorbance limits for petroleum jelly sold in the U.S., both for products applied directly to food (under federal regulation 21 CFR 172.880) and for food-contact materials. These UV tests detect PAHs at very low concentrations. In petroleum jelly that meets FDA standards, total PAH content is estimated at around 1 part per million or less, excluding certain less harmful compounds.
The EU takes a similar but slightly different approach, requiring that petroleum jelly used in cosmetics demonstrate a full refining history showing PAHs have been adequately removed. The key takeaway: the petroleum jelly you buy at a pharmacy has been refined to a pharmaceutical standard and is not the same substance as raw petroleum, despite sharing an origin.
Why It Works So Well on Skin
Petroleum jelly’s composition explains why it’s been a skin care staple for over a century. Those long, saturated hydrocarbon chains are hydrophobic, meaning they repel water. When you apply a layer to your skin, it creates a physical barrier that dramatically slows moisture loss. In lab testing, petroleum jelly reduced water loss through skin to just 14% of normal over 24 hours, outperforming virtually every other occlusive moisturizer tested. This is why dermatologists recommend it for dry, cracked skin, healing wounds, and protecting against windburn or diaper rash.
Because the molecules are chemically inert and too large to penetrate deeply into skin, petroleum jelly sits on the surface rather than being absorbed. It doesn’t deliver active ingredients the way a serum or lotion might. Instead, it locks in the moisture your skin already has and shields it from external irritants. This simplicity is actually its strength: with no fragrances, preservatives, or active compounds, pure petroleum jelly rarely causes allergic reactions or irritation.