Seborrheic Dermatitis SD 脂溢性皮炎

Seborrhoeic Dermatitis SD is a common, chronic, inflammatory dermatosis that has a predilection for the scalp, facial creases and large flexures including the ano-genital area. It affects adults of all ages and often runs a relapsing course. It is a chronic complaint, punctuated with flares and requiring long term treatment.

Seborrheic Dermatitis 6An unsuually extensive eruption covering the entire face.
We are grateful towards this patient’s parents for sending us the photos via WeChat and giving us consent for these photos to be used as a testimonial.

The cause of SD is unclear, but increasing evidence supports a pathogenic role for lipophilic Malassezia yeasts, which was first proposed by Louis Charles Malassez in 1874 [1], whose name is given to the genus of yeasts that are present in lesional skin in SD and dandruff. This was supported by studies showing that relapse of SD and dandruff was associated with reappearance of the lipophilic Malassezia yeasts on the skin [2]. However, these yeasts are not conventional pathogens as they are part of the normal skin microbiome and the mechanisms whereby they trigger diseases remains unclear. Malassezia are primarily found in the infundibulum of the sebaceous gland where lipids, their main energy source, are freely available. They usually exist as skin commensals in a state of symbiosis; the reason this balance is disturbed is unclear.

脂溢性皮炎Seborrheic dermatitis (SD)是一种常见的慢性炎症性皮肤病，通常发生在头皮、面部皱褶和皮肤弯曲处，包括肛门和生殖器区域。它可以影响各个年龄段的人，并且通常呈现反复发作的过程。这是一种慢性的疾病，伴随着急性发作，并需要长期的治疗。

目前尚不清楚引起脂溢性皮炎的原因，但越来越多的证据支持亲脂的马拉色菌（Malassezia）酵母在其发病机制中的致病作用。这一理论最早由Louis Charles Malassez在1874年提出，并且他的名字命名了那些在脂溢性皮炎和头皮屑病患者的皮肤病变中存在的酵母菌属。研究表明，脂溢性皮炎和头皮屑病的复发与亲脂的马拉色菌在皮肤上的再次出现相关[2]。然而，这些酵母菌并不是传统的病原体，因为它们是正常皮肤微生物组的一部分，它们引发疾病的机制尚不清楚。马拉色菌主要存在于皮脂腺的导管内，在那里脂类是它们的主要食物能源，并且通常作为皮肤的共生菌存在；然而，为何这种平衡会被打破尚不清楚。

Reference

  1. Malassez L. Note sur le champignon du pityriasis simple. Arch Physiol 1874;1:451–9.
  2. Hay R. Malassezia, dandruff and seborrhoeic dermatitis: an overview. Br J Dermatol2011;165(Suppl. 2):2–8.

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