Ichthyosis vulgaris is by far the most common form of ichthyosis and results from mutations in FLG, the gene encoding filaggrin. Regardless of severity, the onset of scaling in ichthyosis vulgaris tends to occur after 2 to 3 months of age (not at birth) and may become more prominent during childhood or adolescence. Fine, white scales, often without much erythema, predominate on the exterior surfaces of the extremities, especially the legs. The scaling of patients with ichthyosis vulgaris is most severe on the lower extremities and during cold months. The palms and soles tend to be mildly thickened as well in this semi-dominant common skin disorder.