One ingredient, answered six ways.

Every post here takes a single ingredient and asks the two things a label cannot tell you: what it actually does, and whether that changes depending on who is putting it on.

The first half is the ordinary answer, written from the trials that exist and honest about what they did not measure. A number of these ingredients are sold on a claim the evidence supports weakly or not at all, and saying so is more useful than adding another enthusiastic paragraph to a search result full of them.

The second half is the part general skincare writing leaves out, because a single article has to pick one reader. What moves for someone pregnant, someone breastfeeding, someone postpartum, someone trying to conceive and someone with PCOS, and which body published the instruction that moved it. Where nobody has published one, the post says that rather than filling the gap with an inference.

These are the long form ones, and they are not the whole answer. The catalogue carries a shorter entry for every flagged ingredient in the database, which is the thing to reach for when you are standing in a shop holding a bottle. A post here is for the evening you want to understand why the answer is what it is.