Question
Why do sunscreens show a percentage when creams do not?
The single most useful distinction on a personal care shelf, and it turns on what the front of the box claims.
Part of Sensitive skin
Two tubes on the same shelf. One lists zinc oxide 20 percent in a boxed panel near the top. The other lists twenty ingredients in order and no number anywhere.
Nothing about the chemistry explains that. The claim on the front does.
Two categories, one shelf
A cosmetic cleanses, beautifies or alters appearance. Its label gives an ingredient list in descending order of quantity, and that is the whole of what it must tell you about amount.
An over-the-counter drug does something to the body. A sunscreen filters UV. A skin protectant, in the regulation’s own words, “temporarily protects injured or exposed skin or mucous membrane surfaces from harmful or annoying stimuli”. Both are drug claims.
A drug carries a Drug Facts panel, and for a topical product the labelling rule requires it to state the proportion of each active ingredient.
That is the entire mechanism. Percentages appear because a claim was made, not because the ingredient is special.
The same ingredient, both ways
Zinc oxide is the clearest demonstration. In a mineral sunscreen it is an active, permitted up to 25 percent, and the number is printed. In a foundation using it for opacity, it is a cosmetic ingredient somewhere in the list with no number at all.
Titanium dioxide does the same double duty at the same 25 percent ceiling, and a great many white or pale products contain it purely as a pigment.
Identical mineral, two regulatory identities, one shelf.
Why this is worth carrying around
Most of the frustration people have with ingredient lists comes from wanting quantities and being given order. The cosmetics label guide is largely about living with that.
The Drug Facts panel is the exception, and knowing where the line falls tells you in advance which questions a product can answer. If the front of the box makes a protection claim, expect a number. If it makes a beauty claim, do not.
It also tells you where the inactive ingredients are hiding. On a drug product the list below the panel is everything that is not the active, and for someone tracking down a reaction that is usually the more interesting list. The page for skin that reacts to everything takes the same approach.
Sources
- 21 CFR 201.66: Format and content requirements for OTC drug product labeling US Food and Drug Administration, via eCFR · ecfr.gov Requires products marketed without discrete dosage units, such as topicals, to state the proportion of each active ingredient.
- 21 CFR 352.10: Sunscreen active ingredients US Food and Drug Administration, via eCFR · ecfr.gov Sets the permitted concentration of each sunscreen active, including zinc oxide and titanium dioxide up to 25 percent.
- 21 CFR 347.3: Definitions US Food and Drug Administration, via eCFR · ecfr.gov Defines a skin protectant drug product as one that temporarily protects injured or exposed skin from harmful or annoying stimuli.