Benzoyl peroxide

Benzoyl peroxide is the ingredient in most over-the-counter acne treatments. It is also, under a completely separate regulation, permitted to bleach flour and the milk that becomes several named cheeses.

Those two facts have almost nothing to do with each other, and both are worth knowing.

On skin, with a number attached

The acne regulation permits benzoyl peroxide at 2.5 to 10 percent, and lists Salicylic acid at 0.5 to 2 percent and sulfur at 3 to 10 percent as the alternatives.

Because acne treatment is a drug claim, the product carries a Drug Facts panel and must state the proportion of the active. So the strength is printed, which is unusual for something sold beside cosmetics. The cosmetics label guide covers where that line falls.

The 2.5 percent end of the range is worth noticing. It is the lowest permitted strength and it is a real product rather than a token one, which matters for anyone whose skin reacts badly at higher concentrations.

The marketing copy is also regulated

This is the part that surprises people. The labelling regulation does not merely permit claims, it supplies the words and the label is assembled from them. The product must say “For the” and then “management” or “treatment”, then “of acne.” Beyond that it may add a phrase built by picking from lists: one of “Clears,” “Clears up,” “Clears up most,” “Dries,” “Dries up,” “Dries and clears,” “Helps clear,” “Helps clear up,” “Reduces the number of,” or “Reduces the severity of”, followed by one or more of “acne blemishes,” “acne pimples,” “blackheads,” or “whiteheads”.

Those are not a copywriter’s inventions. They are selections from a list in the Code of Federal Regulations.

It also prescribes the warnings, including that irritation and dryness are more likely if another topical acne medication is used at the same time, and that if irritation occurs you should use only one at a time.

That is a genuinely useful sentence to have read, because stacking actives is the single most common way people make their own skin worse. The page for skin that reacts to everything takes the same view.

The cheese

Separately from all of the above, benzoyl peroxide is affirmed as generally recognised as safe as a bleaching agent in food. The permitted uses are flour, the milk used for a specific list of cheeses including blue, Gorgonzola, Parmesan, Provolone, Romano, Asiago and Swiss, and Whey that has been coloured with Annatto.

The cheese standard sets the limit precisely: not more than 0.002 percent of the weight of the milk being bleached.

Two details make it more interesting than a bare permission.

Vitamin A must be added back. Bleaching destroys vitamin A and its precursors in the milk, and the standard requires the curd to be supplemented to compensate. That is the same nutrient the site covers as Retinyl palmitate, arriving from an unexpected direction.

Artificial colouring is then forbidden. A producer who bleaches this way may not simply colour the result back. The regulation closes that loop deliberately.

None of this appears on the cheese label, because it is a processing step on an ingredient rather than an ingredient in the finished food.

During pregnancy

Benzoyl peroxide is one of the acne actives people ask about most during pregnancy, usually after reading something about the oral retinoids, which are an entirely different class of drug taken a different way.

We are not going to answer it here, and that is deliberate rather than evasive. It is a clinical question that depends on the strength, the area covered and the individual, and the person with your notes in front of them is the one to ask. The page on reading labels during pregnancy is narrow on purpose about which questions a label can settle, and this is squarely outside it.

What a label can tell you is which active is in there and at what strength, and that is worth having before the conversation rather than after.