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

翻译人员: Siqi Gao 校对人员: Helen Chang

Here in this abundant forest,

在这片茂密的丛林里，

Malassezia is equipped with everything it could ever need.

马拉色菌拥有绝佳生存条件，

Feasting constantly, it’s in paradise.

这里如天堂般供它欢宴作乐。

But wait— what’s this?

但等等——这是什么？

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

事实上，马拉色菌是一种酵母，

它在我们所有的头皮上定居和进食。

on all of our scalps.

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

它在近一半的人群中， 导致了头皮屑的产生。

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

那么，为何有些人的头皮屑比较多？

And how can it be treated?

而我们又该怎么处理它呢？

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

我们也许认为我们是独立个体， 但我们其实是一个部落，

Our skin hosts billions of microbes.

我们皮肤表面定植着众多微生物。

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

马拉色菌自我们出生时便很快地 在我们的皮肤上定居。

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

毛囊，全身毛发从这些小凹陷中长出来，

make for especially popular living quarters.

并打造出一个特别友好的生存空间。

Malassezia are fond of these hideouts because they contain glands

马拉色菌特别喜欢这些藏身之处， 因为这里包含了腺体。

that secrete an oil called sebum

而这种腺体能分泌一种油脂，亦称皮脂。

that’s thought to lubricate and strengthen our hair.

普遍认为，这能使我们的头发 变得顺滑和强韧。

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

马拉色菌进而以我们皮肤的 蛋白质和油脂为食。

And because of its many sebum-secreting follicles,

因为头皮有许多分泌油脂的毛囊，

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

所以它是我们全身最多油脂的地方之一，

and consequently, one of the yeastiest.

同时也是酵母最多的地方。

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

当这些酵母在头皮上大吃大喝时， 头皮屑也随之产生。

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

因为皮脂是由饱和脂肪酸 和非饱和脂肪酸共同组成的。

Saturated fats neatly pack together.

饱和脂肪酸整齐地排列在一起。

Unsaturated fats, on the other hand,

相反，非饱和以双键

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

以双键不规则地连接在一起。

Malassezia eat sebum by secreting an enzyme

马拉色菌分泌一种酶，

that releases all of the oil’s fatty acids.

分解皮脂中的所有脂肪酸。

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

但他们只以饱和脂肪酸为食， 剩下了非饱和脂肪酸。

These irregularly shaped leftovers soak into the skin

而这些不规则非饱和脂肪酸 渗入皮肤，

and pry its barrier open, allowing water to escape.

破开了皮肤屏障，让水分外渗。

The body detects these breaches and responds defensively,

身体检测到水分流失 并做出防御性反应，

causing the inflammation that gives dandruff it’s itch.

发生炎症反应， 产生令人发痒的头皮屑。

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

它同时也使皮肤细胞增生， 以修复损伤的屏障。

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

通常，我们皮肤的外表面或表皮

completely renews itself every two to three weeks,

每两到三周就会完全更新一次 。

Epidermal cells divide, move outwards, die,

表皮细胞分裂、外移、凋亡，

and form the skin’s tough outer layer,

形成皮肤坚韧的屏障，

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

并以肉眼无法看到的 单细胞逐渐脱落。

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

但是对于头皮屑，细胞会迅速产生 以修复破损的屏障，

meaning they don’t mature and differentiate properly.

这就意味着它们不能 正常成熟和分化。

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

相反，它们会在毛囊周围 形成又大又油的团块，

that are shed as visible flakes.

并脱落成我们所看到的头皮屑。

This is how Malassezia’s voracious appetite

头皮屑正是由于马拉色菌嗜油脂

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

以及我们对它副产品的反应而产生。

Currently, the most effective way to get rid of dandruff

通常，摆脱头皮屑最有效的方法是

is by using antifungals in things like shampoos,

用含抗真菌成分的洗发露

applied directly to the scalp, to kill Malassezia.

直接抹在头皮上去杀死马拉色菌。

For those who experience dandruff,

对于那些有头皮屑的人来说，

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

皮脂分泌物通常随着人一生的 激素水平的变化而变化。

due to hormonal changes.

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

尽管马拉色菌在每个人身上 的定植程度都差不多，

not everyone gets dandruff.

但并不是每个人都有头皮屑。

Some people are more susceptible.

有些人会更加容易产生皮屑。

Exactly why is unclear.

而原因尚未明确。

Do people with dandruff have a certain genetic predisposition?

有头皮屑的人有明确的遗传易感性吗？

Is their skin barrier more permeable?

非饱和脂肪酸是否 更容易渗入他们的皮肤？

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

目前，科学家正在研究 有头皮屑的人群是否

lose more water through their scalps,

会因为头皮屑而丢失更多水分，

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

或是否因此促进皮肤细胞的增殖。

Researchers are learning that Malassezia communicate with our immune system

研究人员发现马拉色菌通过 一种名为氧化脂素的油性分子

using small, oily molecules called oxylipins that regulate inflammation.

与我们的免疫系统传递信息， 从而调节炎症反应。

If they can find a way to inhibit inflammatory oxylipins

如果他们能找到一种能阻断 炎性氧化脂素产生的方法，

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

或者能促进抗炎物质的生成， 新的治疗方案就能研发出来了。

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

科学家同时也在研究 马拉色菌对于我们来说

with Malassezia.

是不是也有好处。

They hypothesize that dandruff,

他们猜测头皮屑在

which can be uncomfortable and embarrassing for us,

给我们带来不适与尴尬的同时，

creates a reliable, oily food source for the yeast.

也为马拉色菌提供足够的油脂来源。

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

但头皮屑不具有传染性， 也没有对我们的健康造成很大威胁。

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

而马拉色菌似乎很擅长 保护自身领地，即我们的皮肤,

from other, more harmful microbes like Staphylococcus aureus.

不会受到如金黄色葡萄球菌 这些有害微生物的伤害。

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

因此，虽说围绕这些问题， 科学家已经解开了谜底，

surrounding this condition, it must be said:

但还是必须要说：

dandruff remains a head-scratcher.

头皮屑依旧让人挠头。