What causes dandruff, and how do you get rid of it? - Thomas L. Dawson

譯者: Alexis Young 審譯者: Amanda Zhu

Here in this abundant forest,

在這片富饒的森林中，

Malassezia is equipped with everything it could ever need.

馬拉色擁有一切所需，

Feasting constantly, it’s in paradise.

盛宴不斷，似在天堂。

But wait— what’s this?

但是等等，這是什麼？

In fact, Malassezia is a type of yeast that lives and dines

事實上，馬拉色是一種酵母菌，

它在我們的頭皮上生活和吃飯。

on all of our scalps.

And in about half of the human population, its activity causes dandruff.

它的活動讓一半的人口長頭皮屑。

So, why do some people have more dandruff than others?

那麼為什麼有些人的頭皮屑比較多？

And how can it be treated?

又要怎麼治療？

We might consider ourselves individuals, but we’re really colonies.

我們可能認為自己是個體， 但我們其實是殖民地。

Our skin hosts billions of microbes.

我們的皮膚上住著數十億微生物。

Malassezia yeasts make themselves at home on our skin shortly after we’re born.

我們出生後不久就有馬拉色酵母菌 搬到我們的皮膚上住。

Follicles, the tiny cavities that grow hairs all over our body,

遍佈全身的毛髮都是從毛囊長出來的，

make for especially popular living quarters.

毛囊也是馬拉色菌最愛的住所。

Malassezia are fond of these hideouts because they contain glands

馬拉色菌之所以喜歡這些藏身之處， 是因為它們含有一種腺體，

that secrete an oil called sebum

會分泌一種叫做皮脂的油，

that’s thought to lubricate and strengthen our hair.

一般認為這種油能潤滑和強韌毛髮。

Malassezia evolved to consume our skin’s proteins and oils.

馬拉色菌進化為 以皮膚的蛋白質和油為食。

And because of its many sebum-secreting follicles,

由於皮膚有很多分泌皮脂的毛囊，

our scalp is one of the oiliest places on our body—

頭皮就成了全身最油的地方之一，

and consequently, one of the yeastiest.

也因而成為酵母菌最多的地方之一。

As these fungi feast on our scalp’s oils, dandruff may form.

這些真菌酵母在頭皮上大快朵頤時， 頭皮屑就可能會形成。

This is because sebum is composed of both saturated and unsaturated fatty acids.

這是因為皮脂由飽和脂肪酸 和不飽和脂肪酸組成。

Saturated fats neatly pack together.

飽和脂肪的結構整齊緊密，

Unsaturated fats, on the other hand,

然而不飽和脂肪含有雙鍵，

contain double bonds that create an irregular kink in their structure.

在結構中產生不規則的扭結。

Malassezia eat sebum by secreting an enzyme

馬色拉菌會分泌一種酶，

that releases all of the oil’s fatty acids.

將油脂分解為脂肪酸來吃，

But they only consume the saturated fats, leaving the unsaturated ones behind.

他們只吃飽和脂肪， 把不飽和脂肪放在一邊。

These irregularly shaped leftovers soak into the skin

這些形狀不規則的剩菜滲入皮膚，

and pry its barrier open, allowing water to escape.

撬開屏障，讓水逸出。

The body detects these breaches and responds defensively,

身體會偵測到這些破壞， 並作出防禦性的發炎反應，

causing the inflammation that gives dandruff it’s itch.

頭皮屑會癢就是因為發炎。

It also makes the skin cells proliferate to repair the damaged barrier.

頭皮的皮膚細胞也會增生， 以修復損壞的屏障。

Usually, our skin’s outer surface, or epidermis,

通常身體的皮膚的表面， 也就是表皮，

completely renews itself every two to three weeks,

每兩到三週會完全更新一次，

Epidermal cells divide, move outwards, die,

表皮細胞會分裂，向外移動，死亡，

and form the skin’s tough outer layer,

形成皮膚堅韌的外層，

which gradually sheds off in single cells far too small to see.

然後逐漸脫落，

細胞一個一個地脫落， 小到眼睛看不到。

But with dandruff, cells churn out quickly to correct the broken barrier,

但為了修補損壞的屏障， 頭皮細胞必須快速增生，

meaning they don’t mature and differentiate properly.

造成細胞未適當地成熟和分化，

Instead, they form large, greasy clumps around the hair follicle

而在毛囊周圍形成一團一團的油脂，

that are shed as visible flakes.

脫落時是一片一片的，眼睛看得見。

This is how Malassezia’s voracious appetite

馬拉色菌貪婪的胃口 和我們的身體對它副產品的反應

and our bodies reaction to its by-products lead to dandruff.

就是長頭皮屑的原因。

Currently, the most effective way to get rid of dandruff

目前，擺脫頭皮屑最有效的方法

is by using antifungals in things like shampoos,

是使用抗黴菌的洗髮精，

applied directly to the scalp, to kill Malassezia.

直接用在頭皮上，殺死馬拉色菌。

For those who experience dandruff,

對於有這種苦惱的人，

it usually comes and goes as sebum secretions vary throughout one's lifetime

頭皮屑通常會來來去去，

因為皮脂分泌物多寡 在一生中會因荷爾蒙的變化而改變。

due to hormonal changes.

But despite the fact that Malassezia colonize everyone to a similar extent,

儘管馬拉色菌多多少少都會 殖民在每個人頭上，

not everyone gets dandruff.

但並不是每個人都會有頭皮屑，

Some people are more susceptible.

有些人較易有這種困擾，

Exactly why is unclear.

確切原因尚不清楚。

Do people with dandruff have a certain genetic predisposition?

會長頭皮屑的人是否有某些特殊基因？

Is their skin barrier more permeable?

他們皮膚的屏障滲透率更高嗎？

Scientists are currently investigating if people with dandruff do, in fact,

科學家目前正在研究

頭皮屑患者的頭皮是否真的更易脫水？

lose more water through their scalps,

and whether this is what’s leading their skin cells to proliferate.

而頭皮細胞是否因此而增生？

Researchers are learning that Malassezia communicate with our immune system

研究人員最近得知，

馬拉色菌使用稱為氧脂素的 油性小分子與免疫系統溝通，

using small, oily molecules called oxylipins that regulate inflammation.

而氧脂素可調節發炎反應。

If they can find a way to inhibit inflammatory oxylipins

如果能有辦法抑制 引起發炎反應的氧脂素，

and boost anti-inflammatory ones, they could develop new treatments.

同時增加抗發炎的氧脂素， 他們就可以開發新的療法。

Scientists are also investigating if there’s any benefit to our relationship

科學家們也在研究

馬拉色菌對我們是否有益處。

with Malassezia.

They hypothesize that dandruff,

他們提出的假設是，

which can be uncomfortable and embarrassing for us,

儘管頭皮屑讓人不舒服和尷尬，

creates a reliable, oily food source for the yeast.

對酵母菌來說，卻是可靠 又富含油脂的食物來源。

But dandruff isn’t contagious or a great threat to our health.

但頭皮屑不會傳染， 對我們的健康也沒什麼威脅。

And Malassezia seem to excel at defending their territory, our skin,

馬拉色菌好像也很擅長 保護他們的領地——我們的皮膚，

from other, more harmful microbes like Staphylococcus aureus.

免受金黃色葡萄球菌 及其他有害微生物的危害。

So, while scientists have gotten to the bottom of many mysteries

因此，儘管科學家已經揭開 圍繞這種疾病的許多謎團，

surrounding this condition, it must be said:

但我們還是要說：

dandruff remains a head-scratcher.

頭皮屑還是讓我們不停搔頭。