The stratum corneum (SC) which is the outermost layer of epidermis, functions as a barrier against water loss and entry of microorganisms and other environmental agents The SC consists of several layers of “corneocytes”, encased in lipid lamellae, held together by specialized intercellular cell adhesion structures called corneodesmosomes. changes in the lamellar lipid composition, corneocyte size or shape, corneodesmosome number and SC thickness leads to changes in the epidermal permeability barrier function. Sebum normally influences this intercellular organisation to aid desquamation. But in dandruff, altered corneodesmosomal hydrolysis disrupts lipid organization and disturbs the desquamation process, leading to aberrant barrier function.Consistent with this, dandruff patients have more reactive (higher itch perception or flaking) than controls to topical applications of histamine or oleic acid to the scalp. These observations indicate that disrupted epidermal barrier function contributes to the aggravation of dandruff.
Apart from the theories mentioned above, the following theories are known to worsen the dandruff: