Hair Loss: Understanding the Root Causes and What Your Body May Be Telling You

Hair loss can feel frustrating and confusing, especially when it seems to happen without a clear reason. The reality is that hair loss usually does not have just one cause. Instead, it often develops from a combination of genetic, hormonal, nutritional, inflammatory, medical, and lifestyle factors that influence how hair follicles grow and cycle over time (Oiwoh et al., 2024; Wang et al., 2024).

Understanding these underlying contributors can help you and your healthcare provider identify the most likely drivers and create a more effective plan to support hair health.

Common Types of Hair Loss

Before exploring root causes, it helps to understand that several different forms of hair loss exist.

Androgenetic alopecia (pattern hair loss) is the most common type in both men and women. It is influenced by genetics and hormones, particularly sensitivity to androgens, but factors such as inflammation, nutrition, and lifestyle may also contribute (Oiwoh et al., 2024; Liu et al., 2024).

Telogen effluvium is another common form and usually causes diffuse shedding across the scalp. It typically occurs several months after a physical or emotional stressor such as illness, infection, surgery, childbirth, crash dieting, or medication use (Szendzielorz & Śpiewak, 2025; Saini & Mysore, 2021).

Alopecia areata is an autoimmune condition in which the immune system attacks hair follicles, often leading to patchy hair loss. It may occur in people with a genetic susceptibility and can be triggered by stress or illness (Bahashwan & Alshehri, 2024; Rajabi et al., 2018).

Finally, scarring alopecias involve inflammation that damages and permanently destroys hair follicles. One example is central centrifugal cicatricial alopecia (CCCA), which has been linked to genetics, inflammatory processes, and certain hair-care practices (Green et al., 2023).

Nutritional Deficiencies and Hair Loss

Hair follicles are among the fastest-growing cells in the body, so they require a steady supply of nutrients to function properly.

Deficiencies in iron, zinc, vitamin D, B vitamins, vitamin A, vitamin C, vitamin E, and selenium have all been associated with various types of hair loss (Almohanna et al., 2018; Ahmed et al., 2025; Wang et al., 2024). These nutrients support cell growth, immune regulation, and hair follicle function.

Iron deficiency, in particular, is one of the most commonly identified contributors to hair shedding.

Vitamin D deficiency has also been linked with several forms of alopecia, including androgenetic alopecia, telogen effluvium, and alopecia areata, although research is still ongoing to determine how much supplementation improves regrowth (Saini & Mysore, 2021; Ahmed et al., 2025).

Biotin supplements are frequently marketed for hair growth, but true biotin deficiency is rare. When it does occur—often due to gastrointestinal disorders or certain medications—hair loss may improve with supplementation (Almohanna et al., 2018).

In some cases, overall under-nutrition, restrictive dieting, or eating disorders can lead to multiple nutrient deficiencies that manifest as hair loss along with other skin and nail changes (Rallis et al., 2024).

Lifestyle and Environmental Factors

Lifestyle factors can also influence hair health.

Research suggests that smoking, unhealthy diet patterns, and obesity may increase the risk of early-onset pattern hair loss. These factors may affect hair follicles through increased oxidative stress, inflammation, and hormonal changes (Liu et al., 2024; Wang et al., 2024).

Certain hair-care practices, such as tight hairstyles that pull on the hair (traction) or chemical relaxers, have been linked to an increased risk of scarring hair loss conditions like CCCA (Green et al., 2023).

Environmental exposures such as pollution, chronic toxin exposure, and excessive alcohol intake may also disrupt the hair growth cycle, although research in this area is still developing (Wang et al., 2024).

Medical Conditions Linked to Hair Loss

Hair loss can sometimes be a clue that an underlying health condition is present.

Hormonal conditions such as polycystic ovary syndrome (PCOS) can lead to increased androgen levels and are commonly associated with female pattern hair loss (Carmina et al., 2019).

Research has also found connections between early-onset pattern hair loss and metabolic syndrome, insulin resistance, high cholesterol, and cardiovascular disease, suggesting that hair loss may sometimes serve as a visible marker of deeper metabolic health issues (Oiwoh et al., 2024; Liu et al., 2024).

In certain scarring alopecia conditions such as CCCA, associations have been reported with type 2 diabetes, abnormal lipid levels, and uterine fibroids (Green et al., 2023).

Autoimmune diseases can also play a role. Alopecia areata occurs when the immune system mistakenly attacks hair follicles, and it may occur alongside other autoimmune conditions such as type 1 diabetes or rheumatoid arthritis (Bahashwan & Alshehri, 2024).

Inflammation and the Immune System

Inflammation appears to play an important role in many types of hair loss.

Low-grade micro-inflammation around hair follicles has been observed in androgenetic alopecia and may interact with hormones and nutrition to influence follicle health (Oiwoh et al., 2024; Wang et al., 2024).

In scarring alopecias such as CCCA, chronic inflammation damages follicles and eventually replaces them with scar tissue (Green et al., 2023).

In alopecia areata, a complex immune response involving T cells and inflammatory signaling molecules leads to an attack on the hair follicle (Rajabi et al., 2018).

Stress, Sleep, and Emotional Health

Psychological stress can influence hair growth in several ways.

Stressful life events, anxiety, and emotional strain are commonly reported triggers for both telogen effluvium and alopecia areata (Bahashwan & Alshehri, 2024; Rajabi et al., 2018).

Chronic stress may also increase cortisol levels, disrupt sleep, and worsen metabolic and inflammatory processes in the body—factors that can indirectly influence hair health (Oiwoh et al., 2024; Liu et al., 2024).

At the same time, hair loss itself can have a profound emotional impact. Studies show that individuals experiencing alopecia often report decreased quality of life and increased psychological distress, which can create a cycle where stress and hair loss reinforce one another (Szendzielorz & Śpiewak, 2025; Gasmi et al., 2023; Dua et al., 2017).

Gut Health and the Microbiome

Research directly linking the gut microbiome to hair loss is still limited. However, gastrointestinal disorders and malabsorption conditions can lead to deficiencies in nutrients such as iron and biotin that are essential for hair growth (Almohanna et al., 2018; Rallis et al., 2024).

Because of this, gut health may indirectly influence hair health through its impact on nutrient absorption and inflammation.

The Big Picture: Hair Loss Is Often Multifactorial

One of the most important insights from the scientific literature is that hair loss rarely has a single cause. Most people experiencing hair loss have multiple overlapping contributors, including genetics, hormones, nutrient status, metabolic health, inflammation, stress, and lifestyle factors (Oiwoh et al., 2024; Wang et al., 2024).

For this reason, a comprehensive evaluation often includes assessing the type of hair loss pattern, reviewing medical history, evaluating nutritional status, screening for metabolic or hormonal conditions, and exploring lifestyle factors such as stress, diet, and hair-care practices.

Understanding these root causes can help guide a more personalized approach to supporting hair health.

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