Squalene peroxide is a potential actor in dandruff condition

In brief

Lipid profile characterization of both healthy and dandruff-affected scalps revealed that overall, there were lower levels of waxes, glycerides, vitamin E and squalene in dandruff zones of dandruff subjects than in control individuals. Squalene, a major sebum component, was significantly more peroxidized in dandruff-affected scalps. Such squalene peroxidation might result from Malassezia scalp colonization. Therefore, increased levels of Malassezia result in increased squalene monohydroperoxide, which in turn penetrates the stratum corneum and stimulates inflammation and keratinocyte proliferation, generating characteristic clinical dandruff signs, such as altered skin barrier function, flakes and itching.

Introduction

Individual predisposition, scalp sebaceous gland secretion and Malassezia yeast scalp colonization are the three major contributing factors usually associated with dandruff, a common scalp flaking disorder. An underlying deficiency in scalp barrier function characterized by abnormal stratum corneum ultrastructure is believed to cause dandruff in pre-disposed individuals.

Sebum and Dandruff

Several observations have evidenced the role of sebum in dandruff etiology. Indeed, dandruff is often associated with a concomitant increase in scalp sebaceous gland activity and almost all Malassezia species require exogenous lipids as nutrients, they are frequently associated with sebum-rich cutaneous areas, such as the scalp. Some sebaceous free fatty acids, such as lauric and sapienic acids, have been described as “antimicrobials”, and could modify the scalp microbiome. Moreover, topical application of 7.5 % oleic acid, a sebum component can induce dandruff-like symptoms. As well, on a culture medium supplemented with sebaceous lipid, Pityrosporum ovale, a representative of the Malassezia genus, have an oxidative effect as measured by lipoperoxide generation, particularly squalene peroxide. Therefore, a large biochemical exploration of selected lipids and oxidative stress markers on normal and dandruff-afflicted scalps is necessary to investigate the biogenesis of dandruff.

Biochemical and lipid profiles of the scalp

In a cohort of 10 non-dandruff and 10 dandruff-afflicted volunteers, lipid profile characterization of both healthy and dandruff-affected scalps revealed that overall, there were lower levels of waxes, glycerides, vitamin E and squalene in dandruff zones of dandruff subjects than in control individuals. However, squalene, a major sebum component, was significantly more peroxidized in dandruff-affected scalps, resulting in significantly higher ratios of squalene monohydroperoxide (SQOOH)/squalene. This increased ratio was observed when comparing dandruff-affected zones of dandruff subjects to both their non-affected zones and control subjects (Figure 1).

Figure 1. The squalene monohydroperoxide/squalene (SQOOH/SQ) ratio was increased on dandruff-affected zones of the validation cohort. SQOOH/SQ ratio expressed in ng/lg was shown to augment from non-dandruff zones (NDZ) to dandruff zones (DZ) for the 24 affected subjects. Each point represents an individual measurement, blue horizontal lines represent the median at each scalp zone. Values between the two sites for each subject are linked with black lines.

Conclusion

Lipid profile characterization of both healthy and dandruff-affected scalps showed a large increase in levels of squalene monohydroperoxide and of malondialdehyde, suggesting an emerging trend of amplified oxidative stress in dandruff-affected scalps, similar to that observed for acne-affected skin and for scalp seborrheic dermatitis. Such squalene peroxidation might result from Malassezia scalp colonization. Therefore, increased levels of Malassezia result in increased squalene monohydroperoxide, which in turn penetrates the stratum corneum and stimulates inflammation and keratinocyte proliferation, generating characteristic clinical dandruff signs, such as altered skin barrier function, flakes and itching.

Reference

Jourdain R et al. Exploration of scalp surface lipids reveals squalene peroxide as a potential actor in dandruff condition. Arch Dermatol Res. 2016 Apr;308(3):153-63.