FLG and Dry skin: The mechanisms by which filaggrin deficiency may result in ‘dry skin’ have been discussed.30,31 The fact that FLG haploinsufficiency is not independently associated with xerosis per se in this cohort17 may conflict with the hypothesis that FLG null mutations result in dry skin because of a dose reduction in hygroscopic amino acids,30,31 the so-called ‘natural moisturizing factor’.