Petrolatum

Petrolatum is a semi-solid mixture of hydrocarbons refined from petroleum. It is the most effective occlusive available in skincare, and the ingredient that attracts more misinformation than almost any other.

How it works

Petrolatum forms a continuous, water-repelling film on the skin surface. Studies have measured reductions in transepidermal water loss of up to 99 percent, which no other single ingredient approaches.

The mechanism is entirely physical. It does not penetrate meaningfully, does not react with anything, and does not participate in skin biology. It sits on top and stops water leaving.

That is also why it works so well after damage. Water loss is what stalls barrier recovery, and petrolatum stops it while the skin repairs itself.

The "byproduct of petroleum" objection

Petrolatum's origin is real and worth stating: it is refined from crude oil.

The concern usually raised is contamination with polycyclic aromatic hydrocarbons, which are carcinogenic. This is legitimate for unrefined petroleum products.

Cosmetic-grade petrolatum is highly refined and tested. In the EU it is permitted only where the full refining history is known and it can be shown not to be carcinogenic. Pharmaceutical-grade material meets pharmacopoeial standards. The distinction between refined cosmetic petrolatum and crude petroleum residue is enormous.

It does not suffocate skin

Skin does not respire through its surface in any meaningful sense. Oxygen for the epidermis comes from the blood supply beneath, not from the air above. Occlusion does not deprive skin of anything it needs.

It does not dry skin out

A persistent claim holds that petrolatum causes dependency or dries skin over time. There is no mechanism for this and no evidence supporting it.

The confusion may come from the fact that petrolatum alone adds no water. Applied to fully dry skin it seals in dryness. Applied to damp skin, or over a humectant, it seals in moisture. That is a technique issue, not a property of the ingredient.

Comedogenicity

Petrolatum is generally rated non-comedogenic in testing. That said, a heavy occlusive layer over skin that is already congested can worsen the picture for some people, and texture preference is a legitimate reason to choose otherwise.

Where it genuinely excels

Post-procedure care, damaged or fissured skin, very dry conditions, and as a barrier over irritating actives. It is the reference standard against which other occlusives are measured, and it is inexpensive, which is part of why it is so often disparaged in favour of costlier alternatives that do the job less well.