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.

一头健康的头发有如下特征：丰满、光泽，没有头屑或其它可见损伤。那么，是什么使你的至高无上的头发不再那么健康呢？从某种意义上说，它可能是你身体某部健康出了问题的先兆，当然也可能是你头发吹得太多了。

一夜白发

我们可能都听说过一夜白发的故事：某人在经历了可怕的外伤后，一夜醒来突然发现他原本乌黑、或棕褐或红或金色的头发变白了。那么，是否出了什么问题呢？据Arielle Kauvar博士，纽约一个著名的皮肤科医生说，它可能很简单，什么也没发生。Kauvar说，头发变白的唯一原因是根部黑色素的逐步减少，而一夜变白并没有黑色素的转移等生理事件发生。当然， 一个人身体或情绪上的伤害也能导致头发的变化，疾病或压力会令头发由长到不长，数月后，那些头发可能会脱落。所以，如果头发开始脱落，白的还是那么多，那么应该引起重视了。

颜色灰白

当一些人年近40，头发还能保持自然光泽时，另一些人却发现他们的头发20多岁时一个样。这和一个人和身体健康与否没有必然联系，这和各人父母头发变灰年纪有关。Kauvar说，如果你的父母头发变灰早，那么你也会早。和你的年龄一样，头发根部的黑色素也会逐年丧失，在你生出的新发里，黑色素也不如年轻时那么多。这种变化在白种人里面尤其明显，50%的白种人在50岁上下时头发会变灰。

严重的掉发

每天早上发现大把大把地脱发，是身体某部位有状况的一个预警。每天掉大约100根头发是正常的。但如果你掉的更多的话，那么你的头发最少有10万个小泡，这就要注意收集一些早上掉下的头发以观察你的头发变化了。因为这些小泡都有不同的生长规律，一些头发的掉下，都会有新的头发在此生长出来。所以，除非你的头发开始明显地变少或开始出现秃点，那就可能是头发出了状况，不再如自然般健康了。

明显的稀薄

如果你缺铁或蛋白质（正常情形下，是由不正常的饮食所致正常热量的流失），就可能会有比较严重的头发脱落现象。这是因为营养不良导致蛋白质失衡（人身体细胞包括头发的骨架），从而导致头发停止生长。如果有更多的头发脱落，而又没有新的头发生出，这样持续数月，就是一个值得重视的事了。活跃的，不活跃的甲状腺疾病都能导致头发的减少，同时当这种病得到控制后，头发就会重新生长。

变秃

长时间脱发可能是你有秃发的遗传，或是你身体出了点问题。遗传秃顶，医学上称为男性秃头症，三分之一的男人都有类似的问题。一般从顶部开始的头发脱落，时间都会较长。秃头区域的自体免疫机能下降，导致某些物质的失衡，从而大范围的秃顶。尽管医生认为秃头和遗传有联系，但真正的成因还是未知的。有秃头的人，头发多长在后脑部分。

头屑

头屑是头发中最重要的未知的一种疾病。人们通常认为头屑意味着头皮或皮肤太干，需要补充水分来使它更好。但是当头屑变多时，就不仅仅是头皮或皮肤干燥的事了。Kauvar说，头屑是头部皮炎的俗称，头屑严重的地方，头皮会呈红色并看上去很油腻。另一种皮肤――牛皮癣，湿疹，也会有相似的症状，肤色变红、发痒、头屑滋生。无论如何，治疗头屑最好的办法就是使用合适的药用洗发水。

干燥，易开叉蓬的、卷的头发多易开叉。经常使用化学染色剂、每天早上直接对着头发吹风，都将给我们的头发带来很大的伤害。直接在太阳下暴晒，也易对头发造成伤害。将头发扎紧如马尾辫，能减少此类的头发伤害，甚至减少秃发。不健康的头发是不健康的饮食的一个信号，出现这种情况就要及时地认真对待你的头发了。缺乏足够的蛋白质，头发就不能长得足够的弹性；同时基本的脂肪酸（在鱼类动物中较多存在）也能使头发更健康。如果你的饮食缺乏这些，那就要试着去多吃这方面的东西了，发质也就能得到改善了。当然，饮食改变头发生长，并取得明显的效果，那就是数月以后了。