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What do ex-British prime minster Gordon Brown, Jackie Onassis, Britney Spears and I all have in common? We all are (or were) nail biters.
It's not a habit I'm proud of. It's pretty disgusting for other people to watch, ruins the appearance of my hands, is probably unhygienic and sometimes hurts if I take it too far. I've tried to quit many times, but have never managed to keep it up.
Lately I've been wondering what makes someone an inveterate nail-biter like me. Are we weaker willed? More neurotic? Hungrier? Perhaps, somewhere in the annals of psychological research there could be an answer to my question, and maybe even hints about how to cure myself of this unsavoury habit.
My first dip into the literature shows up the medical name for excessive nail biting: 'onychophagia'. Psychiatrists classify it as an impulse control problem, alongside things like obsessive compulsive disorder. But this is for extreme cases, where psychiatric help is beneficial, as with other excessive grooming habits like skin picking or hair pulling. I'm not at that stage, falling instead among the majority of nail biters who carry on the habit without serious side effects. Up to 45% of teenagers bite their nails, for example; teenagers may be a handful but you wouldn't argue that nearly half of them need medical intervention. I want to understand the 'subclinical' side of the phenomenon – nail biting that isn't a major problem, but still enough of an issue for me to want to be rid of it.
It’s mother’s fault
Psychotherapists have had some theories about nail biting, of course. Sigmund Freud blamed it on arrested psycho-sexual development, at the oral stage (of course). Typical to Freudian theories, oral fixation is linked to myriad causes, such as under-feeding or over-feeding, breast-feeding too long, or problematic relationship with your mother. It also has a grab-bag of resulting symptoms: nail biting, of course, but also a sarcastic personality, smoking, alcoholism and love of oral sex. Other therapists have suggested nail-biting may be due to inward hostility – it is a form of self-mutilation after all – or nervous anxiety.
Like most psychodynamic theories these explanations could be true, but there's no particular reason to believe they should be true. Most importantly for me, they don't have any strong suggestions on how to cure myself of the habit. I've kind of missed the boat as far as extent of breast-feeding goes, and I bite my nails even when I'm at my most relaxed, so there doesn't seem to be an easy fix there either. Needless to say, there's no evidence that treatments based on these theories have any special success.
Unfortunately, after these speculations, the trail goes cold. A search of a scientific literature reveals only a handful of studies on treatment of nail-biting. One reports that any treatment which made people more aware of the habit seemed to help, but beyond that there is little evidence to report on the habit. Indeed, several of the few articles on nail-biting open by commenting on the surprising lack of literature on the topic.
Creature of habit
Given this lack of prior scientific treatment, I feel free to speculate for myself. So, here is my theory on why people bite their nails, and how to treat it.
Let's call it the 『anti-theory』 theory. I propose that there is no special cause of nail biting – not breastfeeding, chronic anxiety or a lack of motherly love. The advantage of this move is that we don't need to find a particular connection between me, Gordon, Jackie and Britney. Rather, I suggest, nail biting is just the result of a number of factors which – due to random variation – combine in some people to create a bad habit.
First off, there is the fact that putting your fingers in your mouth is an easy thing to do. It is one of the basic functions for feeding and grooming, and so it is controlled by some pretty fundamental brain circuitry, meaning it can quickly develop into an automatic reaction. Added to this, there is a 『tidying up』 element to nail biting – keeping them short – which means in the short term at least it can be pleasurable, even if the bigger picture is that you end up tearing your fingers to shreds. This reward element, combined with the ease with which the behaviour can be carried out, means that it is easy for a habit to develop; apart from touching yourself in the genitals it is hard to think of a more immediate way to give yourself a small moment of pleasure, and biting your nails has the advantage of being OK at school. Once established, the habit can become routine – there are many situations in everyone's daily life where you have both your hands and your mouth available to use.
Understanding nail-biting as a habit has a bleak message for a cure, unfortunately, since we know how hard bad habits can be to break. Most people, at least once per day, will lose concentration on not biting their nails.
Nail-biting, in my view, isn't some revealing personality characteristic, nor a maladaptive echo of some useful evolutionary behaviour. It is the product of the shape of our bodies, how hand-to-mouth behaviour is built into (and rewarded in) our brains and the psychology of habit.
And, yes, I did bite my nails while writing this column. Sometimes even a good theory doesn't help.
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英國前首相戈登·布朗（Gordon Brown）、傑奎琳·甘迺迪（Jackie Onassis）、布蘭妮·斯皮爾斯（Britney Spears）之間有什麼共同點呢？他們都愛（或曾經都愛）咬指甲。
這嗜好我可不喜歡。被別人看到多噁心呀，把雙手的形象全毀了，很可能不衛生，如果咬得太深還會受傷。我也幾次試圖想要戒掉，但從未持之以恆。
最近，我總在想是什麼讓像我這樣愛咬指甲的人惡習難改呢？難道和其他人相比我們意志更薄弱？更神經質？更有欲望？也許心理學研究的文獻能夠給我答案，也許還能給我一些暗示，教我如何自我擺脫這個令人討厭的習慣。
第一次瀏覽文獻就發現了過度咬指甲的醫學術語：「咬甲癖」（onychophagia）。心理學家把它歸於一種衝脈控制問題，即類似強迫症問題。但這僅指極端案例，精神病學對此的幫助頗有成效，對其他過度怪癖也是如此，如：皮膚搔抓症，拔毛癖。我可沒到那種程度，只是和大多數愛咬指甲的人一樣，一直有這樣的癖好，但沒什麼嚴重的不良反應。45%以上的青少年愛咬指甲，比如：青少年可能只佔一小部分，但你不會說他們中一半人需要接受醫學治療。我想要了解這種現象臨床症狀不明顯的一面——咬指甲沒什麼大驚小怪，但它對我來說依然是件大事，得去克服。
都是媽媽的錯
當然，心理學家在咬指甲方面有許多理論。西格蒙德•弗洛伊德（Sigmund Freud）把它歸結於性心理髮育不良，當然是在口腔期。典型的弗洛伊德理論認為，口欲滯留的原因有很多，諸如：餵食不足或餵食過盛、哺乳時間過長、或與母親關係不睦。當然，各原因交錯也導致了諸多症狀的發生：當然，咬指甲是其一，還有為人尖酸刻薄、吸菸、酗酒、喜歡口交。其他理療師建議將咬指甲歸於「內在敵意」——畢竟是某種形式上的自殘——或是緊張焦慮。
像大多心理動力論這樣解釋也許是說的通的，但沒有特別的理由說服我們去相信這些解釋是對的。對我來說最重要的是：他們並沒有任何強有力的說法，如何自己戒掉這個習慣。就母乳餵養的程度而言，我早已過了那時期。甚至在我最放鬆的情況下我也咬指甲，所以似乎也沒有什麼簡單的解決辦法。更不用說，現今沒有證據證明基於這些理論上的治療有任何特別的成效。
可惜在種種猜測之後，也慢慢無從所知了。檢索相關科學文獻只發現一些基於如何治療咬指甲癖的研究。其中一項研究指出：任何讓人們愈發認識到咬指甲這個癖好的治療似乎是有所幫助的，但除此之外並沒有什麼有關該癖好的報導。事實上，幾篇為數不多關於咬指甲的文章公開評述該問題上的文獻嚴重不足。
習慣的奴隸
鑑於之前沒有接受過科學治療，我可以輕鬆地自我省視。所以以下就是我自己的理論，解釋為什麼人們會咬指甲，以及如何治療這個毛病。
讓我們把這個理論稱為「反理論」之理論。我假設沒有特殊的原因引發咬指甲——不是因為什麼母乳餵養、長期焦慮、缺乏母愛。把這些統統都排除的好處是我們不需要在我和戈登、傑奎琳、布蘭妮之間找出一個特別的連接點。我認為：咬指甲僅僅是由於諸多因素引發的——由於隨機變異——一些人形成壞習慣的結合。
首先，有這樣一個事實：把你的手指放進嘴裡是件很容易的事。這是餵養最基本的功能之一。所以它是受一些最基本腦神經元迴路控制的，也就是說它能迅速發展成為一種自動條件反射。此外，對咬指甲有一種「打理」因素——讓指甲始終是短的——這就意味著就短期而言至少它能讓人心情舒暢，即使其主要是讓你的手指苦不堪言。這種獎勵因素同行為者採取的愉悅相結合，意味著這種癖好能夠輕鬆養成；除了手淫之外，真的很難想像有什麼更為直接的方式讓自己愉悅片刻了，而且咬指甲的好處就是在學校這麼做完全沒問題。這種癖好一旦建立，就會變成常規——每個人的日常生活都有許多你都得使用你的雙手和嘴的情況。
把咬指甲當作是一種癖好去理解，對治療的作用並不大，因為遺憾的是我知道擺脫壞習慣有多難。大多數人一天中至少一次會無意識地咬指甲。
在我看來，咬指甲並不是揭示了什麼人格特徵，也不是一些對人類有益進化行為的不良反映。它是我們身體構造的產物，是手對嘴行為如何在人類大腦中建立以及習慣心理的產物。
是的，我在寫這篇專欄的時候確實咬指甲了。有時就算是一個好理論也幫不上忙。
（譯者 Canddi 編輯 丹妮）
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