A healthy head of hair is easy to spot. It’s full, shiny and lustrous with no flakes, frizzies or other visible damage. But what about when your crowning glory isn’t quite so glorious? In some cases, it might be a harbinger of health problems—or it could simply mean that you’re spending too much time with the blow dryer.

White overnight?
We’ve all heard horror stories of someone who, in the aftermath of some terribly traumatic event, woke up to find their formerly brown, red or blond hair turned shockingly white. Well, don’t worry about it happening to you, because, according to Dr. Arielle Kauvar, a New York dermatologist, it simply can’t happen. “The only way for hair to turn gray is a gradual decline in melanin production at the root,” says Kauvar. “There is no biological event that can remove pigment directly from the hair shaft.” However, a physical or emotional trauma can cause a change in the hair. The illness or stress sends actively growing hair into a resting phase, and a couple of months later, all those strands in the resting phase may fall out. So, if the dark hairs fall out and the already white ones remain, the result is hair that looks suddenly grayer.

Going gray
Some people start finding those wiry gray strands as early as their 20s, while others hold onto their natural color well into their 40s. The cause is unrelated to how healthy—or unhealthy—you are. As with so many things, it turns out you can blame (or thank) your parents for the rate at which your hair turns gray. “It’s mostly genetic,” Kauvar says, “so if your parents grayed early, it is likely you will too.” The hair that’s already on your head doesn’t lose pigment. But as you age, there is a decrease in melanin production in the hair bulb (or root). So when new strands start to grow, they may come in with less—or no—pigment, thanks to that decrease in melanin. The change happens most quickly in Caucasians, 50 percent of whom will be at least 50 percent gray by age 50.

Serious shedding
Seeing a swarm of strands in the shower drain every morning isn’t necessarily a cause for alarm—or a signal that anything is wrong with you. It’s totally normal to lose about 100 strands of hair every day. And even if you think you’re losing more than that, remember that your head carries at least 100,000 hair follicles, so it’s possible to collect a handful or two out of the bath or hairbrush without it visibly changing the appearance of your mane. And since those 100,000 or so follicles have different growth phases, even as several strands fall out, dozens of new ones are just on their way in to replace them. So unless you’re starting to notice visible thinning of your hair or bald spots on your scalp, chances are the loss is nothing more than natural, everyday shedding.

Visibly thinning
If you have iron or protein deficiency—common with the caloric deprivation of anyone suffering from an eating disorder—it is not unusual to experience severe hair loss. That’s because the malnutrition forces the body to conserve protein (the building block of all the body’s cells, including the hair) by shutting down hair growth. And since more hair may also be shed—without being replaced—the result can be a noticeable thinning over several months. Thyroid disease (both an overactive thyroid and an underactive one) can also show up as increased hair loss. Once the disease is controlled, hair growth can usually be restored.

Going bald
Really losing your hair can be a sign that you’ve inherited a tendency for baldness, or it could indicate a bigger health issue. Heredity baldness, medically known as androgenetic alopecia, affects up to one third of men. The hair loss—which typically begins at the temples or crown—is permanent. Alopecia areata is an autoimmune disease which can cause anything from smooth bald patches to the loss of all hair on both the head and body. The cause of the disease isn’t known, although some doctors feel there is a genetic link. With this type of alopecia, hair normally grows back.

The flaky stuff
Dandruff is one of hair’s most misunderstood maladies. People often assume that those flakes must mean that the scalp is too dry and that, like skin that’s flaking, it must obviously need more moisture to make it look better. But while some people may indeed suffer from a dry scalp, true dandruff is not a matter of dryness. “Dandruff is the common name for seborrheic dermatitis, an inflammatory condition of the scalp that causes redness and flaking in the areas of the skin that are rich in oil glands,” Kauvar explains. Other skin conditions—such as psoriasis and eczema—can also cause a similar condition in which the scalp gets red, itchy and produces flakes of dandruff. In any case, the best cure is to seek out a medicated (not necessarily moisturizing) shampoo or scalp treatment.

Dull, dry, brittle, and breaking

Hair that looks frazzled, frizzy and fried most likely is just that. We can do tremendous damage by using chemical dyes and permanents as well as by simply aiming the blow dryer at our heads every morning. Like being in the sun, all of these self-inflicted abuses destroy the cuticle and leave hair wide open to damage. Pulling hair into tight braids or ponytails can increase that stress and lead to breakage—or even bald spots. But in addition to being a cue that you need to treat you hair more carefully, unhealthy strands can also be an indicator of an unhealthy diet. Without adequate protein, growing hair strands won’t become as strong and resilient as they should be. And essential fatty acids (found in fish oil supplements, wild salmon, and flax seeds) may also play a role in keeping strands strong, shiny and healthy. If your diet is lacking in them, try increasing your consumption and see if your hair eats it up! Of course, what you eat can only impact hair that is just starting to grow, so it will be several months before any improvements are evident.

一頭健康的頭發有如下特征：豐滿、光澤，沒有頭屑或其它可見損傷。那么，是什么使你的至高無上的頭發不再那么健康呢？從某種意義上說，它可能是你身體某部健康出了問題的先兆，當然也可能是你頭發吹得太多了。

一夜白發

我們可能都聽說過一夜白發的故事：某人在經歷了可怕的外傷后，一夜醒來突然發現他原本烏黑、或棕褐或紅或金色的頭發變白了。那么，是否出了什么問題呢？據Arielle Kauvar博士，紐約一個著名的皮膚科醫生說，它可能很簡單，什么也沒發生。Kauvar說，頭發變白的唯一原因是根部黑色素的逐步減少，而一夜變白并沒有黑色素的轉移等生理事件發生。當然， 一個人身體或情緒上的傷害也能導致頭發的變化，疾病或壓力會令頭發由長到不長，數月后，那些頭發可能會脫落。所以，如果頭發開始脫落，白的還是那么多，那么應該引起重視了。

顏色灰白

當一些人年近40，頭發還能保持自然光澤時，另一些人卻發現他們的頭發20多歲時一個樣。這和一個人和身體健康與否沒有必然聯系，這和各人父母頭發變灰年紀有關。Kauvar說，如果你的父母頭發變灰早，那么你也會早。和你的年齡一樣，頭發根部的黑色素也會逐年喪失，在你生出的新發里，黑色素也不如年輕時那么多。這種變化在白種人里面尤其明顯，50%的白種人在50歲上下時頭發會變灰。

嚴重的掉發

每天早上發現大把大把地脫發，是身體某部位有狀況的一個預警。每天掉大約100根頭發是正常的。但如果你掉的更多的話，那么你的頭發最少有10萬個小泡，這就要注意收集一些早上掉下的頭發以觀察你的頭發變化了。因為這些小泡都有不同的生長規律，一些頭發的掉下，都會有新的頭發在此生長出來。所以，除非你的頭發開始明顯地變少或開始出現禿點，那就可能是頭發出了狀況，不再如自然般健康了。

明顯的稀薄

如果你缺鐵或蛋白質（正常情形下，是由不正常的飲食所致正常熱量的流失），就可能會有比較嚴重的頭發脫落現象。這是因為營養不良導致蛋白質失衡（人身體細胞包括頭發的骨架），從而導致頭發停止生長。如果有更多的頭發脫落，而又沒有新的頭發生出，這樣持續數月，就是一個值得重視的事了。活躍的，不活躍的甲狀腺疾病都能導致頭發的減少，同時當這種病得到控制后，頭發就會重新生長。

變禿

長時間脫發可能是你有禿發的遺傳，或是你身體出了點問題。遺傳禿頂，醫學上稱為男性禿頭癥，三分之一的男人都有類似的問題。一般從頂部開始的頭發脫落，時間都會較長。禿頭區域的自體免疫機能下降，導致某些物質的失衡，從而大范圍的禿頂。盡管醫生認為禿頭和遺傳有聯系，但真正的成因還是未知的。有禿頭的人，頭發多長在后腦部分。

頭屑

頭屑是頭發中最重要的未知的一種疾病。人們通常認為頭屑意味著頭皮或皮膚太干，需要補充水分來使它更好。但是當頭屑變多時，就不僅僅是頭皮或皮膚干燥的事了。Kauvar說，頭屑是頭部皮炎的俗稱，頭屑嚴重的地方，頭皮會呈紅色并看上去很油膩。另一種皮膚――牛皮癬，濕疹，也會有相似的癥狀，膚色變紅、發癢、頭屑滋生。無論如何，治療頭屑最好的辦法就是使用合適的藥用洗發水。

干燥，易開叉蓬的、卷的頭發多易開叉。經常使用化學染色劑、每天早上直接對著頭發吹風，都將給我們的頭發帶來很大的傷害。直接在太陽下暴曬，也易對頭發造成傷害。將頭發扎緊如馬尾辮，能減少此類的頭發傷害，甚至減少禿發。不健康的頭發是不健康的飲食的一個信號，出現這種情況就要及時地認真對待你的頭發了。缺乏足夠的蛋白質，頭發就不能長得足夠的彈性；同時基本的脂肪酸（在魚類動物中較多存在）也能使頭發更健康。如果你的飲食缺乏這些，那就要試著去多吃這方面的東西了，發質也就能得到改善了。當然，飲食改變頭發生長，并取得明顯的效果，那就是數月以后了。