What the percentages on a label mean

We print the percentage of each active on the front of the bottle. That only helps if the number means something to you, so here is how to read it.

What the number is

The percentage is the weight of the ingredient as a share of the finished formula. Ten percent vitamin C means ten grams of ascorbic acid in every hundred grams of serum.

Why higher is not always better

Every active has a range in which it is commonly used. Above that range, irritation tends to rise faster than any benefit. Niacinamide is widely used between 2% and 5%; retinal is used at fractions of a percent because it is far more potent by weight.

You cannot compare across ingredients

Five percent of one ingredient tells you nothing about one percent of another. Compare a percentage only with the usual range for that same ingredient.

What the number does not tell you

• The pH of the formula, which affects how some acids behave.
• What else is in the bottle to keep the active stable.
• How your own skin will respond.

That is why we also tell you who a product suits and when to patch-test. The Ingredients page lists the range we use for each active and the products it appears in.