The diagnosis of androgenic alopecia can be usually established based on clinical presentation in men. In women, the diagnosis usually requires more complex diagnostic evaluation. Further evaluation of the differential requires exclusion of other causes of hair loss, and assessing for the typical progressive hair loss pattern of androgenic alopecia. Trichoscopy can be used for further evaluation. Biopsy may be needed to exclude other causes of hair loss, and histology would demonstrate perifollicular fibrosis.

Because they are not usually associated with an increased loss rate, male-pattern and female-pattern hair loss do not generally require testing. If hair loss occurs in a young man with no family history, drug use could be the cause.

- The pull test helps to evaluate diffuse scalp hair loss. Gentle traction is exerted on a group of hairs (about 40–60) on three different areas of the scalp. The number of extracted hairs is counted and examined under a microscope. Normally, fewer than three hairs per area should come out with each pull. If more than ten hairs are obtained, the pull test is considered positive.

- The pluck test is conducted by pulling hair out "by the roots". The root of the plucked hair is examined under a microscope to determine the phase of growth, and is used to diagnose a defect of telogen, anagen, or systemic disease. Telogen hairs have tiny bulbs without sheaths at their roots. Telogen effluvium shows an increased percentage of hairs upon examination. Anagen hairs have sheaths attached to their roots. Anagen effluvium shows a decrease in telogen-phase hairs and an increased number of broken hairs.

- Scalp biopsy is used when the diagnosis is unsure; a biopsy allows for differing between scarring and nonscarring forms. Hair samples are taken from areas of inflammation, usually around the border of the bald patch.

- Daily hair counts are normally done when the pull test is negative. It is done by counting the number of hairs lost. The hair from the first morning combing or during washing should be counted. The hair is collected in a clear plastic bag for 14 days. The strands are recorded. If the hair count is >100/day, it is considered abnormal except after shampooing, where hair counts will be up to 250 and be normal.

- Trichoscopy is a noninvasive method of examining hair and scalp. The test may be performed with the use of a handheld dermoscope or a video dermoscope. It allows differential diagnosis of hair loss in most cases.

There are two types of identification tests for female pattern baldness: the Ludwig Scale and the Savin Scale. Both track the progress of diffused thinning, which typically begins on the crown of the head behind the hairline, and becomes gradually more pronounced. For male pattern baldness, the Hamilton–Norwood scale tracks the progress of a receding hairline and/or a thinning crown, through to a horseshoe-shaped ring of hair around the head and on to total baldness.

In almost all cases of thinning, and especially in cases of severe hair loss, it is recommended to seek advice from a doctor or dermatologist. Many types of thinning have an underlying genetic or health-related cause, which a qualified professional will be able to diagnose.

Hair loss can be slowed or reversed in its early stages with medication. Medications approved by the United States' Food and Drug Administration (FDA) to treat male-pattern hair loss include minoxidil and finasteride.

Though not as common as the loss of hair on the head, chemotherapy, hormone imbalance, forms of hair loss, and other factors can also cause loss of hair in the eyebrows. Loss of growth in the outer one third of the eyebrow is often associated with hypothyroidism. Artificial eyebrows are available to replace missing eyebrows or to cover patchy eyebrows. Eyebrow embroidery is another option which involves the use of a blade to add pigment to the eyebrows. This gives a natural 3D look for those who are worried about an artificial look and it lasts for two years. Micropigmentation (permanent makeup tattooing) is also available for those who want the look to be permanent.

Alopecia areata is usually diagnosed based on clinical features.

Trichoscopy may aid in establishing the diagnosis. In alopecia areata, trichoscopy shows regularly distributed "yellow dots" (hyperkeratotic plugs), small exclamation-mark hairs, and "black dots" (destroyed hairs in the hair follicle opening).

A biopsy is rarely needed to make the diagnosis or aid in the management of alopecia areata. Histologic findings include peribulbar lymphocytic infiltrate ("swarm of bees"). Occasionally, in inactive alopecia areata, no inflammatory infiltrates are found. Other helpful findings include pigment incontinence in the hair bulb and follicular stelae, and a shift in the anagen-to-telogen ratio towards telogen.

Dietary supplements are not typically recommended. There is only one small trial of saw palmetto which shows tentative benefit in those with mild to moderate androgenetic alopecia. There is no evidence for biotin. Evidence for most other produces is also insufficient. There was no good evidence for gingko, aloe vera, ginseng, bergamot, or hibiscus as of 2011. While lacking both evidence and expert recommendation, there is a large market for hair growth supplements, especially for products that contain biotin.

Many people use unproven treatments, but there is little evidence of the effectiveness of vitamins, minerals, or other dietary supplements regrowing hair or retaining hair.

Commonly, alopecia areata involves hair loss in one or more round spots on the scalp.

- Hair may also be lost more diffusely over the whole scalp, in which case the condition is called diffuse alopecia areata.

- Alopecia areata monolocularis describes baldness in only one spot. It may occur anywhere on the head.

- Alopecia areata multilocularis refers to multiple areas of hair loss.

- Ophiasis refers to hair loss in the shape of a wave at the circumference of the head.

- The disease may be limited only to the beard, in which case it is called alopecia areata barbae.

- If the person loses all the hair on the scalp, the disease is then called alopecia areata totalis.

- If all body hair, including pubic hair, is lost, the diagnosis then becomes alopecia areata universalis.

Alopecia areata totalis and universalis are rare.

A scalp biopsy is essential for the diagnosis of cicatricial alopecia and is the necessary first step, as it can be hard to know the diagnosis for sure without a biopsy. Findings of the scalp biopsy, including the type of inflammation present, location and amount of inflammation, and other changes in the scalp, are necessary to diagnose the type of cicatricial alopecia, to determine the degree of activity, and to select appropriate therapy.

Clinical evaluation of the scalp is also important. Symptoms of itching, burning, pain, or tenderness usually signal ongoing activity. Signs of scalp inflammation include redness, scaling, and pustules. However, in some cases there are few symptoms or signs and only the scalp biopsy demonstrates the active inflammation. The overall extent and pattern of hair loss is noted and sometimes photographed for future comparison. A hair "pull test" is performed to see if growing, or "anagen", where hairs are pulled out easily. The pulled hairs are mounted on a slide and the hair bulbs are viewed with a light microscope to determine how many are growing hairs and how many are resting hairs. In addition, if pustules are present, cultures are taken to identify which microbes, if any, may be contributing to the inflammation. A thorough evaluation that includes all of these parameters is important in diagnosing a cicatricial alopecia and in identifying features in individual patients that will help the selection of therapy.

New diagnostic techniques, such as trichoscopy may be used for non-invasive differential diagnosis of cicatricial alopecia.

Diagnosis and treatment of cicatricial alopecias is often challenging. For this reason, it is helpful to be evaluated by a dermatologist with a special interest or expertise in scalp and hair disorders, and who is familiar with current diagnostic methods and therapies.

Hair care products and shampoos can generally be used with any frequency desired, as long as the products are gentle and non-irritating to the scalp. Hair pieces, wigs, hats, and scarves may be used freely.

There is no standard treatment for alopecia universalis. Many treatments have been explored, including immunomodulatory agents such as imiquimod. Tofacitinib citrate may also have benefits. In June 2014, it was reported that a 25 year old man with almost no hair on his body grew a full head of hair, and eyebrows, eyelashes, facial, armpit and other hair, following 8 months of treatment.

There is currently researching being done to find more treatments dependent on the different pre-existing conditions.

Studies are being conducted in which madarosis can be related to malignancy. A study by Groehler and Rose found that there was a statistical significance between these two. They concluded that patients malignancy lesions on the eyelid have a higher chance of having madarosis than a patient with a benign lesion. They stated that despite the fact that it is significant, the absence of madarosis does not mean the lesion cannot be malignant.

In many leprosy cases, madarosis is a symptom or a quality after diagnosis. However, in India, leprosy is common and researchers report a case of madarosis before diagnosis of leprosy with no skin lesions, only madarosis. This allowed for quicker treatment.

A main reason many people have madarosis is due to the chemotherapy drugs. There was a clinical trial in 2011 that tested an eyelash gel called bimatoprost. This gel enhanced the eyelashes in quantity and thickness. They tested this on 20 breast cancer patients who were undergoing chemotherapy. Results seemed positive, in that the group of people who used the gel had growth of eyelashes after the chemotherapy drugs.

The main diagnosis technique is observing the area. Then blood tests can be done to determine if there is a pre-existing condition. Family history can be considered because some of the related causes/conditions can be inherited.

Improvement or stabilization of the condition has been reported with topical and intralesional corticosteroids, antibiotics, hydroxychloroquine, topical and oral immunomodulators, tacrolimus, and most recently, 5-alpha-reductase inhibitors. In one study, the use of anti-androgens (finasteride or dutasteride) was associated with improvement in 47% and stabilization in 53% of patients

It is commonly seen with certain hair styles or braiding patterns that pull the hairline forcefully towards the vertex of the scalp, and has been reported more often in African American women (as some wear their hair tightly pulled back), in whom it can cause scarring. It has also been seen in female ballerinas, and in cultural traditions where the hair is voluntarily not cut in religious obeisance, the latter caused by progressively increasing weight of the hair itself. Traction alopecia is mechanical in cause, rather than androgenic, and treatment is typically not pharmaceutical. Management includes cessation of the chronic traction, cosmeses, with surgical restoration reserved for more severe cases.

Traction alopecia is a substantial risk in hair weaves, which can be worn either to conceal hair loss, or purely for cosmetic purposes. The former involves creating a braid around the head below the existing hairline, to which an extended-wear hairpiece, or wig, is attached. Since the hair of the braid is still growing, it requires frequent maintenance, which involves the hairpiece being removed, the natural hair braided again, and the piece snugly reattached. The tight braiding and snug hairpiece cause tension on the hair that is already at risk for falling out. Traction Alopecia is one of the most common causes of hair loss in African American women.

Sikh men are also susceptible to traction alopecia if the hair under the turban is tied too tightly for many years.

Other causes include:

- Hairstyle. Although the aforementioned style is one of the culprits, hairstyles such as dreadlocks and single (extension) braids can also have the same effect. Men and women who have suffered from traction alopecia have found that the hair loss occurs most at the hair line—primarily around the temples and the sides of their heads.

- Headgear. Compressive safety helmets worn tightly and closely to the scalp are a cause of traction alopecia. The lining of tightly fitted safety helmets like those worn for activities such as motorcycling, cycling, skiing and snowboarding are responsible for the constant rubbing and tugging of localised areas of the hair and scalp. Frequent wearers or those who use such helmets for prolonged periods seem more likely to suffer traction alopecia.

- Chemicals. A condition known as CCCA (central cicatricial centrifugal alopecia), seen almost exclusively in African American women, can cause extensive hair loss. It is caused by a combination of too much stress (traction) on the hair and the use of harsh relaxers and dyes.

CCCA tends to present itself in the 20s and progresses over 20–30 years. One should consider this diagnosis in African Americans with what appears to be a female-pattern hair loss.

Alopecia universalis can occur at any age, and is currently believed to be an autoimmune disorder, in which a person's immune system attacks the hair follicles. Genetic factors may contribute to AU as approximately 20% of those affected have a family member with alopecia.

Treatments for CCCA remain investigational. Altering hair care practices has not been proven to assist in hair rejuvenation. High-dose topical steroids, antibiotics, immunomodulators such as tacrolimus (Protopic) and pimecrolimus (Elidel), and anti-androgen/5alpha Reductase inhibitors have been used with unknown efficacy.

Important diagnoses to consider include female pattern hair loss (FPHL), chronic telogen effluvium (CTE), and alopecia areata (AA). FPHL is a non-scarring progressive miniaturization of the hair follicle with one of three different characteristic patterns. CTE is an idiopathic disease causing increased hair shedding and bi-temporal recession, usually in middle aged women. AA is an autoimmune attack of hair follicles that usually causes hair to fall out in small round patches.

Methotrexate and corticosteroids are proposed treatments.

Scalp cooling has specifically been used to prevent alopecia in docetaxel chemotherapy, although it has been found prophylactic in other regimens as well. Treatment effects may take time to resolve, with one study showing breast cancer survivors wearing wigs up to 2 years after chemotherapy.

Hair diseases are disorders primarily associated with the follicles of the hair.

A few examples are

- Alopecia

- Bubble hair deformity

- Hair casts

- Hair loss

- hypertrichosis

- Ingrown hair

- Monilethrix

- Premature greying of hair

- Pattern hair loss

- Trichorrhexis invaginata

Many hair diseases can be associated with distinct underlying disorders.

Piedra are fungal diseases.

Hair disease may refer to excessive shedding or baldness (or both). Balding can be localised or diffuse, scarring or non-scarring. Increased hair can be due to hormonal factors (hirsutism) or non-hormonal (hypertrichosis). Scalp disorders may or may not be associated with hair loss.

An androgen-dependent condition, disease, disorder, or syndrome, is a medical condition that is, in part or full, dependent on, or is sensitive to, the presence of androgenic activity in the body.

Known androgen-dependent conditions include acne, seborrhea, androgenic alopecia, hirsutism, hidradenitis suppurativa, precocious puberty in boys, hypersexuality, paraphilias, benign prostatic hyperplasia (BPH), prostate cancer, and hyperandrogenism in women such as in polycystic ovary syndrome (PCOS).

Such conditions may be treated with drugs with antiandrogen actions, including androgen receptor antagonists such as cyproterone acetate, spironolactone, and bicalutamide, 5α-reductase inhibitors such as finasteride and dutasteride, CYP17A1 inhibitors such as abiraterone acetate, gonadotropin-releasing hormone (GnRH) analogues such as leuprolide and cetrorelix, and/or other antigonadotropins such as megestrol acetate and medroxyprogesterone acetate.

Non scarring hair loss, also known as noncicatricial alopecia, is the loss of hair without any scarring being present. This is in contrast to scarring hair loss.

Causes of noncicatricial alopecia include:

- Alopecia areata

- Anagen effluvium

- Androgenetic alopecia

- Dermatopathia pigmentosa reticularis

- Telogen effluvium

- Trichotillomania (Trichotillosis)

Telogen effluvium is a scalp disorder characterized by the thinning or shedding of hair resulting from the early entry of hair in the telogen phase (the resting phase of the hair follicle). Emotional or physiological stress may result in an alteration of the normal hair cycle and cause the disorder, with potential causes including eating disorders, fever, childbirth, chronic illness, major surgery, anemia, severe emotional disorders, crash diets, hypothyroidism, and drugs.

Diagnostic tests, which may be performed to verify the diagnosis, include a trichogram, trichoscopy and biopsy. Effluvium can present with similar appearance to alopecia totalis, with further distinction by clinical course, microscopic examination of plucked follicles, or biopsy of the scalp. Histology would show telogen hair follicles in the dermis with minimal inflammation in effluvium, and dense peribulbar lymphocytic infiltrate in alopecia totalis.

Vitamin D levels may also play a role in normal hair cycle.