Overall, the average rate of hair growth is about 0.38 mm per day [1]. The rate of hair growth varies slightly from person to person and between races with individuals of African descent showing slower hair growth and Asians showing more rapid hair growth [2].

This is a common myth that is not true. Washing your hair frequently does not harm your hair and actually may be helpful. The frequency of hair washings by patients can be influenced by hair, culture, sex, and economics [3]. There is no maximum number of washings per week as long as you regularly condition your hair [3]. You may notice hair falling out during shampooing; however, this is completely normal. The hairs lost are in the resting or telogen phase of the hair cycle and are supposed to fall out to give way to new hairs. Rubbing very hard the hair during washing can damage the hair shaft.

Cutting hair can help reduce split ends, which can leave your hair looking healthier. Your hair, however, is not strengthened by being cut, and it is not useful in the setting of hair loss or thinning.

It is completely normal for some hair to fall out every day. The average woman loses about 50–150 hairs per day [4]. The average man loses about 25–100. The hairs that fall out are replaced by new hairs in a continuous hair cycle. The activity of each individual hair follicle is cyclical and normally unrelated to the other follicles alternating between periods of growth and rest before being shed and replaced by a new hair. Normally about 90% of hair follicles are in the growing phase or anagen, and about 10% are in the resting or telogen phase. In disease states, the hair cycle can be altered which may cause more hair loss than expected.

Yes, just like your scalp hair, it is completely normal for hair to fall out from your eyebrows and eyelashes. Just like your scalp hair, hair from your eyebrows and eyelashes follows the hair cycle, but in these locations, the time frame is a bit different. The growth or anagen phase in these areas lasts for about 1–4 months compared to the scalp where it lasts for multiple years [5]. In addition, eyelashes grow slower and to a shorter maximum length of 6–7 mm [5, 6].

The average woman sheds about 50–150 hairs per day [4]. Most of these hairs are shed during brushing and washing. Daily hair loss becomes abnormal when more than 200 hairs are shed per day [7]. Hair loss may be best visualized using validated visual scales (see page 293) [8]. Excessive hair loss or shedding requires medical evaluation, as it is the primary symptom of a number of hair and scalp diseases.

Increases in the amount of hair loss can be due to a number of diseases, including anagen effluvium, telogen effluvium, alopecia areata, and androgenetic alopecia; however, it can also be due to a change in awareness [4]. Changes in hair length, bathroom lighting, shower flooring, and even anxiety about hair loss can all lead to a change in perception of hair loss [7].

Androgenetic alopecia causes hair thinning with/without an increase in hair shedding. The process results from a shortened growth or anagen phase of the hair cycle. This causes follicular miniaturization leading to shorter, thinner hairs [9].

Studies have shown that increased hair loss occurs in Autumn compared to other seasons [10, 11]. This increase in shedding occurs due to an increased number of hairs entering the resting or telogen phase of the hair cycle in July [10]. This stage occurs about 100 days prior to shedding [10]. This fluctuation in hair shedding may be due to an evolutionary advantage where hair is only shed after keeping the scalp warm in the winter and protecting it from the sun during the summer [10].

This should not cause any alarm and is completely normal. The white bulb is the part of the hair that is closest to the root. This means that the hair was lost at the base and was not broken along the shaft. These hairs are in the resting or telogen phase of the hair cycle, and it is normal to shed them.

Almost everyone’s hair starts to turn white at some point in their life. The change occurs due to changes in melanocytes, which are responsible for your hair color. These are the same type of cells that are responsible for your skin tone [12]. Damage to these cells can result in them producing less pigment which causes hair to lose its original color and turn white. The appearance of gray is due to the mixture of white and pigmented hairs.

It is difficult to estimate when your hair will change color as it varies in everyone. Genetics play an important role in the timeframe. Individuals of African and Asian descent often gray at later ages than Caucasians. In addition, environmental factors such as smoking, excessive alcohol intake, drug use, emotional stress, physical illness, and obesity can all cause you to gray earlier than expected [13, 14]. A traditional rule of thumb states that 50% of people are 50% gray by the age of 50 years; however, recent studies have shown that 6–23% of people are 50% gray by the age of 50 years [15].

Graying of hair is almost always permanent and progressive; however, there are rare reports of spontaneous return to pigmented hair and partial reversals of the process during its early stages. There is no treatment at this time to stimulate the reversal of hair graying [16].

Your hair is one of the innumerable body parts negatively affected by smoking. Smoking negatively affects both your skin and your hair. It results in reduced quality and quantity of hair [17]. Smoking has been associated with premature graying [14] and increased severity of androgenetic alopecia [18].

The sun and the associated UV radiation is damaging to both your hair and your scalp just like it is to your skin. Studies have shown that extended sun exposure may aggravate androgenetic alopecia and cause telogen effluvium [19, 20]. In addition, UV radiation from the sun is known to cause photoaging, which negatively affects both the color and the quality of your hair [21]. The easiest way to protect against sun damage to your hair is by wearing a hat.

It could be a contributing factor. An increase in stress leads to an increase in the production of cortisol, which negatively affects the function and regulation of the hair cycle [22]. This reaction can lead to hair loss under stress. Telogen effluvium is an example of a disease process that results in hair loss due to both physical and mental stress [23]. In addition, psychological stress can lead to premature graying of hair [13].

Vitamin, oligoelements, and amino acid deficiencies can cause changes in hair structure, pigmentation, and even lead to hair loss [24]. Replacement of these factors can aid in the recovery from some hair diseases. However, hair loss can also be due to an excess of some substances such as vitamin A or selenium [24]. You should consult your physician before taking any over-the-counter remedies for your hair loss.

A balanced diet that includes meat, poultry, fish, fruits, and vegetables is one key to healthy hair. Meat and fish are good sources of zinc. Meat, poultry, and fish are among the best sources of iron. Fish are one of the best sources of essential fatty acids. Fruits and vegetables provide antioxidants. All of these substances are beneficial to both the scalp and the hair [25]. Always try to eat organic to avoid possible hormones in meat, eggs, and dairy.

A vegetarian or vegan diet has risks of not having sufficient iron intake. Iron deficiency can have a number of negative effects on your health including on your hair. You may take an iron supplement or eat foods rich in iron to make sure you have sufficient iron in your diet. Foods rich in iron include spinach, legumes, quinoa, and broccoli. Lysine supplementation can help in improving iron absorption. Ask your physician to evaluate your iron levels if you think you could be deficient.

An abrupt interruption of a hormonal contraceptive can cause hair loss or alopecia similar to that seen after childbirth due to telogen effluvium. In addition, alopecia has been reported as a side effect of some hormonal contraceptive methods. Alopecia is listed as a side effect on progestin-containing oral contraceptives [26]. In addition, it is listed as an uncommon side effect (0.1–1.0%) on levonorgestrel intrauterine devices (IUDs), while a large-scale Finnish study found hair loss rates of almost 16% in women using levonorgestrel IUDs [27, 28]. This large difference in number is likely due to the difference in the methods of the studies. The Finnish study was a questionnaire study, while the quoted 0.1–1.0% is based on clinician findings [28]. A more recent study showed no association with levonorgestrel IUDs and hair loss [29].

Menopausal hormone changes cause decreased hair diameter, growth rate, and percentage in the growth or anagen phase [30]. The prevalence of androgenetic alopecia increases in postmenopausal women.

Yes, your thyroid can be the cause of your hair loss. Thyroid function (TSH, T3, T4) is routinely checked in patients suffering from hair loss. Telogen effluvium is an example of one type of hair loss that can result from abnormal thyroid function. Hypothyroidism can also lead to coarse, brittle hair [31]. Before getting these tests, notify your doctor if you are taking biotin supplements. Biotin can affect the results of these tests, so you may need to stop taking biotin for about 2 days prior to undergoing the test [32].

Unfortunately, no. Hair analyses have not been shown to be useful in diagnosing causes of hair loss. Studies have shown large variations in results even when the same person provides a sample [33].

Hair loss has many different causes. A medical consultation with your dermatologist is the first step. He or she will take a thorough medical and family history and perform a focused physical exam that should include trichoscopy. In addition, he or she may choose to run additional tests including but not limited to a biopsy and blood workup depending on the suspected diagnosis.

Dry hair can be a sign of damaged hair. The damage is most likely in the lipid outer layer of the hair shaft, which, when lost, causes the hair to feel dry. Dry hair is a sign of damaged hair, and it is normally not associated with reduced synthesis of the sebum that keeps the skin oily.

Scalp pain or trichodynia is a relatively common problem, affecting around 20% of women and 9% of men seeking attention for hair-related problems [34]. The sensation can be diffuse throughout the scalp or can affect defined regions of the scalp [35]. It appears to be due to the release of a molecule called substance P [36]. Anxiety may also play a role in the perception of the painful sensation [34]. Patients suffering from hair loss, especially from telogen effluvium, alopecia areata, and androgenetic alopecia, have increased rates of trichodynia [37–39].

An inability to grow long hair is most often due to an issue of increased fragility of the hair shaft. This can be due to environmental factors such as excessive processing, styling, and heating.

Alopecia areata has a variable, typically relapsing, remitting course that is usually persistent, especially when hair loss is extensive [40]. Patients suffering from alopecia areata have the potential to regrow hair for many years possibly throughout their whole life since the disease process does not destroy the hair follicle [40]. According to one study, the initial attack lasts less than 1 year in about 50% of patients, but all patients eventually experience a relapse [41]. The same study showed that 50% of patients whose disease began before puberty developed alopecia totalis and 23% of those whose disease began after puberty eventually developed alopecia totalis [41]. Patients with alopecia totalis or universalis have about a 41% chance of 90% hair regrowth according to a recent South Korean study [42].

Alopecia areata is associated with a number of comorbidities; however, patients with alopecia areata are generally healthy [40]. Patients with alopecia areata have an increased incidence of depression, anxiety, several autoimmune disorders, inflammatory skin disorders, nail changes, and atopic diseases [43–48].

The chances are low. A Chinese study found that about 1.1% of children of patients with alopecia areata are also affected by the disease [49]. Individuals diagnosed at an earlier age have a higher chance of first-degree relatives being affected [49].

In cases of alopecia areata, hair regrowth may occasionally be white at first. The hair usually, but not always, gradually returns to its natural color.

Alopecia areata incognita was first described in 1987 [50]. It is a variant of alopecia areata without the classic patches characterized by an acute diffuse shedding of telogen hairs. It is frequently misdiagnosed as telogen effluvium or androgenetic alopecia [51].

Shedding hairs shorter than 3 cm is a sign of androgenetic alopecia. Androgens shorten the duration of the anagen growing phase of the hair cycle. This results in a process called follicular miniaturization leading to shorter, thinner hairs [9]. This disease is progressive if untreated.

Male and female pattern hair loss are the most common forms of hair loss. These diseases are also known as “androgenetic alopecia” because the hair loss is caused by two main factors: androgens (male hormones) and genetic predisposition. Androgen production increases after onset of puberty; therefore, the first noticeable signs of androgenetic alopecia usually begin in adolescence. The most important hormone for the development of this form of hair loss is dihydrotestosterone, or DHT, which is a very potent androgen. DHT is produced locally at the hair follicle by conversion from testosterone. The conversion of testosterone to DHT is regulated by the enzyme 5-alpha-reductase. This enzyme is the target of the common drug used to treat hair loss called Propecia (finasteride). The follicles that are predisposed to androgenetic alopecia produce greater amounts of DHT compared to follicles that are not affected [52].