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Skin allergy / Review of other studies
Atopic dermatitis skin has a weakened barrier that allows topical drugs up to about 800 Dalton (tacrolimus 822 Da, the ascomycin derivative SDZ ASM 981 811 Da) to work, whereas the same molecules and larger ones (cyclosporine, 1202 Da) are not effective applied topically to normal skin.
Moderate evidence: Narrative synthesis of separately published clinical trials, not a new experiment; treated by the authors as the named exception to their own 500 Dalton rule.
Source: Bos & Meinardi 2000, Experimental Dermatology Link to this fact
Information, not medical advice. See also: myths we won’t tell you.