Which list correctly orders these retinoids from WEAKEST to STRONGEST as they appear at the same concentration?
a.Tretinoin, retinaldehyde, retinol
b.Retinol, tretinoin, retinaldehyde
c.Retinaldehyde, retinol, tretinoin
d.Retinol, retinaldehyde, tretinoin
Explanation
Retinoids must be converted into retinoic acid in the skin to act. Retinol takes two conversion steps, retinaldehyde takes one, and tretinoin (retinoic acid) is already active. Fewer steps means stronger and faster effect at the same percentage.
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