Common causes of thinning hair and hair loss—and how you can address it

Medically reviewed by Rosanna Sutherby, PharmD on November 23, 2019. Written by Kathryn Wall. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Thinning hair can be distressing to experience, especially when you don’t know what’s causing it. A decrease in hair density and shrinking hair follicles can both cause thinning hair. If you're wondering how to stop thinning hair, it's important to understand the possible reasons behind it.

Common causes

High testosterone

High testosterone has been linked with a kind of hair loss known as androgenetic alopecia in both men and women [1]. This disorder can be inherited, which is why a family history of hair loss may increase your risk for thinning hair or hair loss [2].

Test your testosterone level at home.

Malnutrition and vitamin deficiencies

Malnutrition and vitamin deficiencies—like low levels of vitamin D—can cause hair loss [3]. Hair follicles need proteins, vitamins, and other nutrients for their continuous growth cycle.

Test your vitamin D level at home.

Thyroid conditions

Thyroid conditions like hypothyroidism (underactive thyroid) can also contribute to thinning hair and hair loss [4][5]. Among U.S. adults, Hashimoto’s disease—a kind of immune system malfunction—is the most common cause of hypothyroidism. It affects 10 times more women than men.

Check for indicators of thyroid dysfunction.

Heavy metal exposure

Exposure to some heavy metals—like mercury—can result in hair loss, as well as other symptoms (such as fatigue, depression, insomnia, irritability, and memory loss) [6]. Fish consumption is a common source of chronic mercury exposure (fish like shark, swordfish, tilefish, and king mackerel are known to have a high mercury content). People who work in the manufacturing industry are also at risk of exposure to mercury vapor [7].

Check for mercury exposure at home.

Stress

Stress can also play a role in sudden and significant hair loss [8]. In a condition known as telogen effluvium, significant stress or a triggering life event can cause hair follicles to stop growing actively and enter the resting phase [9]. Alopecia areata is another condition where your body's immune system attacks hair follicles [10]. One of the triggers for this condition is also severe stress. Often, once this stress is under control, both of these conditions can be reversible, and your hair could grow back.

Test for indicators of chronic stress.

Environmental triggers

Certain environmental triggers can accelerate hair thinning, such as sun exposure, over styling, and overuse of shampoos and hair products [11]. By limiting these environmental exposures, you can eliminate some of the major contributors to thinning hair.

Related health conditions

Androgenetic alopecia

Androgenetic alopecia is a genetic condition characterized by gradual hair loss and thinning [12]. It occurs in both men and women, but the pattern of hair loss is sex-specific. Men tend to lose hair from the front of their hairline and extending to the top of their heads, while women tend to lose hair mainly from the top of their heads. Thyroid disease, iron deficiency anemia, and malnutrition can also mimic androgenetic alopecia symptoms.

Alopecia areata

Alopecia areata is characterized by patchy baldness over any part of the body, including the scalp, eyebrows, armpits, or facial hair [13]. It is an autoimmune disease where your immune system attacks hair follicles. There is a strong genetic link, and alopecia areata usually develops in childhood or teenage years.

Telogen effluvium

Telogen effluvium is hair loss from the scalp that occurs up to three months after a triggering event [14]. It is non-scarring (reversible) and dispersed. It is usually short-lived, often only lasting up to six months. Stress is one of the major causes of this condition.

Regular thyroid screening is key: A healthy thyroid is important for many of your body’s functions (and thyroid disorders are linked with thinning hair). The American Thyroid Association recommends thyroid screening in adults beginning at age 35 years and every 5 years after [15]. Get the Everlywell Thyroid Test

What you can do about thinning hair and hair loss

Consult your healthcare provider if you’re experiencing thinning hair. Physicians can determine whether the hair loss is nonscarring (noncicatricial) or scarring (cicatricial), and recommend treatment options. Nonscarring hair loss is reversible, but scarring hair loss is permanent and non-reversible.

How common is hair loss? Hair loss is incredibly common, with almost 50% of men affected by the age of 50 and 38% of women affected after the age of 70 [16].

A physical examination focuses on the hair and scalp [17]. A pull test involves an examiner applying gentle traction to about 40–60 hairs. If more than 10% of the hairs (4–6 hairs) are removed from the scalp, the active hair shedding warrants further diagnosis and investigation. Patients that present with hair loss are often screened for nutritional deficiencies, as well.

Because malnutrition and vitamin deficiencies can be related to hair loss [18], a well-balanced diet is essential for managing and slowing thinning hair. Certain foods high in protein and micronutrients (such as eggs, leafy greens, and fortified whole-grains) can also help promote hair growth. There are also cosmetic options to consider, such as wigs or hair transplants [19].

Vitamin levels and hair loss: Scientific studies show a connection between low vitamin D levels and some kinds of hair loss like androgenetic alopecia. Symptoms may improve with supplementation [20]. Test for low vitamin D

Common questions

My hair is thinning. What's causing this?

There are several possible reasons for thinning hair and hair loss. Common causes of thinning hair in women include hormonal fluctuations (such as pregnancy or menopause). Genetics, increased stress, or nutritional deficiencies are common causes of thinning hair in men as well as women.

How can I stop thinning hair?

Eliminating environmental triggers—such as stress, overstyling, sun exposure, and chemical exposure—may help. Nutrient deficiencies can also cause persistent hair loss. A well-balanced diet is incredibly important for managing hair loss.

What can I do for thinning hair?

Consult your healthcare provider to determine the underlying cause of thinning hair or loss. Stress is often the main culprit of sudden hair loss. By reducing stress, hair loss can often be reversed within a short time period. If other underlying medical conditions are present, your physician can help develop a treatment plan.

What can I do for thinning hair on the top of my head?

Determining the underlying cause for thinning hair is important. Cosmetic solutions and topical treatments are the main solutions for thinning hair on the top of the head. In the case of age-related hair thinning, consult with a dermatologist to learn more about topical treatments that stimulate hair regrowth.