Science Focus ( Issue 21)

By Henry Lau 劉以軒 13 Myth #1: Only teenagers get acne. Fact: While it is true that the many cases of acne outbreaks occur during puberty, acne outbreaks can occur anytime beyond age 20. For instance, acne outbreaks can occur before menstruation or during pregnancy in females, probably due to hormonal changes [3, 4, 11]. Stress can also lead to acne through the elevated level of stress hormones [2]. However, the underlying cause of postadolescent acne is largely unknown [11]. Myth #2: Washing your face more often will cure acne. Fact: While this seems logical, there is no strong evidence that washing more would cure acne [10]. Antibacterial skin cleansers and acidic cleansing bars might have marginal effect on mild acne [10]. However, excessive face washing may unnecessari ly remove sebum on the skin sur face that normal ly functions to retain moisture. It dr ies the skin and causes the compensatory overproduction of sebum, therefore defeating the purpose of the treatment [10]. Myth #3: Eating oily food will cause acne. Fact: There is not enough scientific evidence yet to prove that dietary fat [13], or any single food [14], can cause acne. However, speaking of diet, previous studies indicated that reducing glycemic load on diet might improve the outcome of acne [10]. Acne also seemed to be correlated with obesity [2, 10], but no evidence has proven yet that dietary restriction reduces acne [10]. More study is needed to show the causation between diet and acne [2]. Myth #4: It is OK to pop your pimple. Fact: It’s not okay to pop your pimple on your own. Popping them with bare hands can bring more bacteria to the area and worsen the inflammation. Dermatologist are trained to do proper acne removal with sterile instruments if needed, although this is usually done only when other treatments don’t work [15]. Generally, if your acne condition persists or worsens, it’s advisable to seek advice from a dermatologist. A combination of topical retinoid and antimicrobial therapy can be prescribed to suppress inflammation by blocking the inflammatory pathways in our body and control l ing the growth of C. acnes [16]. It can also reduce the blockage of pi losebaceous units by inhibiting the prol iferation of keratinocytes [16]. 你試過一覺醒來望向鏡子，然後發現臉上新長了幾顆痘 痘嗎？有的話，那可能就是暗瘡了（英文叫「acne」或「acne vulgaris」）。 暗瘡由皮膚發炎所致，準確來說是發生在毛囊皮脂腺單 位（pilosebaceous units）的炎性反應，這些毛孔負責長 出毛髮和製造皮脂。暗瘡常見於毛囊皮脂腺單位豐富的位 置，包括面部，還有額頭、頸、上胸和肩膀 [1]。暗瘡的形成通 常涉及以下三個現象：皮脂分泌過盛、皮膚細菌感染和毛囊 異常角質化 [2]。 皮脂分泌過盛 如前文所述，毛孔分泌皮脂，它是一種保護皮膚免受細 菌傷害和防止皮膚乾燥的油性液體。可是，過多的皮脂會塞 住毛孔，形成暗瘡。皮脂分泌受多個因素控制，其中一個經 常被研究的是雄性激素 [2, 3]，它們是青春期引起身體變化 的性激素。雄性激素水平會在青春期大幅提升，它們亦能導 致皮脂過度分泌 [3, 4]，這正是為什麼暗瘡通常出現於青春 期的原因。 皮膚細菌感染 有 些 細 菌 居 住 在 我 們 皮 膚 表 面，其 中 一 種 是 Cutibacterium acnes （舊稱 Propionibacterium acnes [5]），它們可能參與暗瘡的形成。 C. acnes 以皮脂作為食 物，當有多餘皮脂的時候細菌種群能生長和大量分裂。被 多餘皮脂塞住的毛孔就可能被 C. acnes 感染，加劇周邊的 炎性反應並引起暗瘡 [2, 6]。 透過比較暗瘡患者和健康人士鼻上毛囊皮脂腺單位中 的 C. acnes 菌株，研究人員指出一些菌株與暗瘡有著密切 關聯，亦有一些是與健康皮膚有關的 [7]。基因組分析揭示 了這些菌株都有一些獨特的基因元件，它們可能對形成暗瘡 或維持皮膚健康起作用 [7]。對這些菌株的功能作進一步研 究可能有助闡明暗瘡的病理，最終有助發展出針對性的療 法 [7]。 毛囊異常角質化 角質化是一種名為角質細胞的皮膚細胞硬化的過程， 當中涉及角蛋白 [8]。這些硬化了的細胞會被推至皮膚表面 形成保護層，例如角質層，保護皮膚免受感染、乾燥和物理 應力影響 [8]。可是，在暗瘡患者上會觀察到毛囊過度角質 化的現象，即是過多的角蛋白令角質層異常地加厚 [6, 9]， 形成角質化塞子堵住毛囊，提供無氧環境令 C. acnes 滋生 [10, 11]。另一方面， C. acnes 亦會透過分泌丙酸影響角質化，令皮膚細胞 有著異常的形狀 [2]。這些過程都會導致 粉刺形成。