When the ability to smell goes away

当嗅觉消失时

About 14 years ago, Chrissi Kelly lost her sense of smell. She had traveled to the Czech Republic to visit family and caught some virus. Months later, when she still couldn’t smell, she made the rounds to doctors, including her general practitioner and an ear, nose and throat specialist, trying to find answers. She was diagnosed with anosmia (smell loss), and like many patients with her condition, was told she’d have to learn to live with it. But for her, the loss was catastrophic. “After about six months of complete loss, I was just climbing the walls, and I did not feel like myself anymore,” she says.

大约 14 年前，克丽丝·凯利（Chrissi Kelly）失去了嗅觉。当时她前往捷克共和国探亲，期间感染了一种病毒。几个月后，当她依然无法闻到气味时，她四处求医，包括咨询全科医生和耳鼻喉科专家，试图寻找答案。她被诊断出患有嗅觉缺失症（anosmia），并像许多患有此病的患者一样，被告知必须学会与它共存。但对她来说，这种丧失是灾难性的。“在完全失去嗅觉大约六个月后，我简直快要崩溃了，我觉得自己不再是原来的我了，”她说。

Researchers estimate that up to 22 percent of the population lives with smell impairments, like hyposmia (partial smell loss) or anosmia (complete smell loss). And many others live with smell disorders like phantosmia, in which a person picks up phantom smells, or parosmia, where typically pleasant scents like coffee or shampoo begin to register as highly unpleasant (think feces or vomit). Yet the conditions have been poorly understood, underdiagnosed and often minimized by clinicians.

研究人员估计，高达 22% 的人口患有嗅觉障碍，例如嗅觉减退（部分嗅觉丧失）或嗅觉缺失（完全嗅觉丧失）。还有许多人患有嗅觉紊乱，如幻嗅症（phantosmia，即闻到不存在的气味）或嗅觉倒错（parosmia，即咖啡或洗发水等通常令人愉悦的气味开始变得极其难闻，类似于粪便或呕吐物的味道）。然而，这些病症一直未得到充分的理解和诊断，且经常被临床医生轻视。

The pandemic changed that. Covid brought unprecedented attention—and research interest — to the sense of smell. There have been 780 million reported cases of Covid-19 since December 2019 (and many more unreported), according to the World Health Organization, and smell loss is a well-known symptom. In one 2023 survey published in the journal Laryngoscope, 60 percent of individuals with Covid experienced smell loss, most temporarily, but some over the longer term. With Covid causing millions of noses worldwide to malfunction at roughly the same time, the virus spurred newfound appreciation for, and research into, this critical sense. As scientists learn more about the way that the sense of smell operates, evidence is mounting that smell is deeply tied not only to quality of life but also to brain health.

疫情改变了这一切。新冠病毒为嗅觉带来了前所未有的关注和研究兴趣。根据世界卫生组织的数据，自 2019 年 12 月以来，全球已报告了 7.8 亿例新冠肺炎病例（还有更多未报告病例），而嗅觉丧失是一个众所周知的症状。在 2023 年发表于《喉镜》（Laryngoscope）杂志的一项调查中，60% 的新冠患者经历了嗅觉丧失，大多数是暂时的，但也有一些是长期的。由于新冠病毒导致全球数百万人的鼻子在同一时间出现功能障碍，这种病毒激发了人们对这一关键感官的重新认识和研究。随着科学家们对嗅觉运作方式的深入了解，越来越多的证据表明，嗅觉不仅与生活质量密切相关，还与大脑健康息息相关。

The undervalued sense

被低估的感官

In the 19th century, French brain researcher Paul Broca argued that humans had traded a keen sense of smell for higher intellect, labeling olfaction “the bestial sense.” His ideas led to decades of scientific neglect. Modern research has proved him wrong. Smell enriches life and directs our behavior. It helps parents and children to bond, warns us of environmental dangers, and anchors emotional memory. “Humans are actually quite good at smelling,” says Swedish psychologist Jonas Olofsson, author of The Forgotten Sense: The New Science of Smell and the Extraordinary Power of the Nose.

19 世纪，法国大脑研究员保罗·布罗卡（Paul Broca）认为，人类为了更高的智力而牺牲了敏锐的嗅觉，并将嗅觉称为“兽性感官”。他的观点导致科学界对此忽视了数十年。现代研究证明他是错的。嗅觉丰富了生活并引导着我们的行为。它有助于父母与子女建立联系，提醒我们注意环境危险，并巩固情感记忆。“人类实际上非常擅长嗅觉，”瑞典心理学家乔纳斯·奥洛夫森（Jonas Olofsson）说，他是《被遗忘的感官：嗅觉的新科学与鼻子的非凡力量》（The Forgotten Sense: The New Science of Smell and the Extraordinary Power of the Nose）一书的作者。

We smell by detecting airborne molecules that bind to specialized receptors in the nasal cavity. Millions of olfactory neurons in the upper nose detect these odorants, then send electrical impulses via the olfactory bulbs, which create a sensory map in the brain—basically, a system to identify, distinguish, and remember scents. Unlike vision or hearing, smell directly signals brain areas responsible for emotion (the amygdala) and memory (the hippocampus), which could be why smells can strongly trigger memories. Furthermore, the olfactory bulbs are now known to be among the few brain regions that create new neurons during adulthood. This is thought to help the brain deal with constantly changing environments. The olfactory bulbs are also the most vulnerable part of the brain—a potential entry site for viruses, bacteria, toxins and perhaps even microplastics.

我们通过检测与鼻腔内特殊受体结合的空气分子来感知气味。鼻腔上部的数百万个嗅觉神经元检测到这些气味分子，然后通过嗅球发送电脉冲，在大脑中创建感官地图——本质上是一个识别、区分和记忆气味的系统。与视觉或听觉不同，嗅觉直接向负责情绪（杏仁核）和记忆（海马体）的大脑区域发送信号，这可能就是为什么气味能强烈触发记忆的原因。此外，已知嗅球是成年后少数能产生新神经元的大脑区域之一。这被认为有助于大脑应对不断变化的环境。嗅球也是大脑中最脆弱的部分——是病毒、细菌、毒素甚至微塑料的潜在入侵点。

After losing her sense of smell, Kelly searched for insight and commiseration. Finding neither, she founded two nonprofit patient groups. Along the way, she also became a community scientist, co-publishing more than 30 academic papers with researchers. Kelly describes our olfactory bulbs as “two little earthworms lying in their crypts,” located on the bottom surface of the brain’s frontal lobes, directly above the nasal cavity. “These crypts have got little holes underneath, through which the olfactory nerves grow, like roots coming through the bottom of a pot in the garden,” she says. Hair-like extensions from the olfactory nerves protrude into the inside of the nose’s mucous membrane. Olfactory support cells surround and nourish each nerve cell.

在失去嗅觉后，凯利寻求洞察和共鸣。由于两者都未找到，她创立了两个非营利性患者组织。在此过程中，她也成为了一名社区科学家，与研究人员共同发表了 30 多篇学术论文。凯利将我们的嗅球描述为“躺在墓穴里的两条小蚯蚓”，位于大脑额叶的底面，就在鼻腔的正上方。“这些墓穴下方有小孔，嗅神经通过这些小孔生长，就像花园里花盆底部的根一样，”她说。嗅神经的毛发状延伸物突入鼻粘膜内部。嗅觉支持细胞包围并滋养着每一个神经细胞。

Reasons for smell loss

嗅觉丧失的原因

Some people lose their sense of smell for no known reason. Others lose it after a virus attacks the olfactory support cells. When the support cells regenerate (four to six weeks later, on average), smell returns. Smell loss can also be due to a head injury that damages the olfactory nerves or causes inflammation. Allergies and sinus infections can cause swelling and inflammation that lead to smell loss. Sometimes the problem clears when the inflammation does. Less fortunate folks, like Kelly, suffer assaults to their olfactory nerves that cause lasting damage.

有些人无缘无故地失去了嗅觉。另一些人则是在病毒攻击嗅觉支持细胞后失去嗅觉。当支持细胞再生时（平均四到六周后），嗅觉就会恢复。嗅觉丧失也可能是由于头部受伤损坏了嗅神经或引起炎症所致。过敏和鼻窦感染会导致肿胀和炎症，从而导致嗅觉丧失。有时，当炎症消退时，问题就会解决。像凯利这样不幸的人，他们的嗅神经遭受了攻击，导致了持久的损伤。

And sometimes, smell loss can be a harbinger of deeper trouble. Dave, a wine lover living in the Midwest who asked that his last name be withheld for privacy, says losing his sense of smell 20 years ago was an inconvenience, but he managed. “I faked it,” he says, of taking wine tours in the Napa and Sonoma Valleys with his wife, and on a cruise that kicked off with wine-filled days in Nice, France. After years of doctors telling him they couldn’t find anything wrong with him, he began to experience a slowed gait and tremors, and was diagnosed with Parkinson’s disease.

有时，嗅觉丧失可能是更深层问题的先兆。戴夫（Dave）是一位住在中西部的葡萄酒爱好者，他要求隐去姓氏以保护隐私。他说，20年前失去嗅觉虽然很不方便，但他还是应付过来了。“我假装能闻到，”他说，他曾与妻子一起参加纳帕谷和索诺玛谷的葡萄酒之旅，还参加了一次以法国尼斯葡萄酒日为开端的游轮旅行。在多年被医生告知找不到任何问题后，他开始出现步态缓慢和震颤，最终被诊断出患有帕金森病。

There are a lot of unknowns about the earliest—or prodromal—stages of Parkinson’s, says Ethan G. Brown, a neurologist at the University of California, San Francisco’s Movement Disorders Clinic. “We don’t know when neurodegeneration actually starts,” he says. A defining feature of the disorder is a major loss of dopamine-producing cells in a brain region called the substantia nigra, and new imaging tools suggest the damage begins years before clear symptoms. Scientists suspect toxic proteins that damage the substantia nigra may first…

加州大学旧金山分校运动障碍诊所的神经学家伊桑·G·布朗（Ethan G. Brown）表示，关于帕金森病的早期（或前驱）阶段，还有很多未知数。“我们不知道神经退行性变究竟从何时开始，”他说。该疾病的一个显著特征是被称为黑质的大脑区域中产生多巴胺的细胞大量丧失，而新的成像工具表明，这种损伤在明显症状出现前几年就已经开始了。科学家怀疑，损害黑质的毒性蛋白质可能首先……