Do carrots decrease sebum?

Possible. Yes or No?: Our body takes apart ingested materials, physically & chemically, down to tiny molecules (called digestion), to protect us from most threats, then rebuilds them into structures we need to stay alive as we constantly both tear-down & re-build our body. Could molecules from carrots (mostly starch) ↑ sebum (mostly fat molecules)? Possible because body converts sugars to fat for storage. See Evidence

Myth: Since carrots contain carotene which the body has the ability to make into vitamin A, and very high doses of vitamin A or its relatives (famously isotretinoin) cause loss of the sebaceous glands, there's a "pop" idea that eating carrots suppresses sebum production. You can't make carotene into vitamin A fast enough to get toxic / high levels from doing it.

Yes, if excessive: Carrots are rich in Vitamin A, which helps regulate sebum production. Vitamin A can help reduce excessive sebum production if overstimulated by androgens.