When hair loss shows up alongside always feeling cold and constant tiredness, the three together often point to one underlying cause rather than three separate problems. The most common culprit is an underactive thyroid, but low iron, nutrient gaps, and not eating enough can produce the same pattern. Below is what each cause looks like, and when it is time to get checked.

Any one of these symptoms on its own is common and often harmless. What makes this trio worth attention is that your hair, your body temperature, and your energy are all downstream of your metabolism and your blood's ability to carry oxygen. When all three slip at the same time, it usually means something measurable is off, and most of the causes below are confirmed with a simple blood test and are very treatable.

1. Hypothyroidism (Underactive Thyroid)

What it is: A condition in which the thyroid gland does not make enough thyroid hormone. That hormone sets the pace of your metabolism, so when it runs low, many body systems slow down at once.

Why it happens: The most common cause is an autoimmune condition called Hashimoto's thyroiditis, in which the immune system gradually reduces thyroid function. It can also follow thyroid surgery, radiation treatment, or certain medications.

Common symptoms: This is the classic fit for the whole trio. Thyroid hormone regulates body temperature, energy, and the hair growth cycle, so an underactive thyroid tends to cause feeling cold when others are comfortable, persistent fatigue, and diffuse hair thinning across the scalp (and sometimes thinning of the outer eyebrows). Other clues include weight gain, dry skin, constipation, and low mood.

Risk factors: A family history of thyroid disease, being female, age over 60, pregnancy in the past year, and having another autoimmune condition.

When to seek evaluation: A TSH blood test, sometimes with free T4, can confirm or rule this out. It is one of the most common and most treatable causes of this symptom pattern, and treatment is a daily thyroid hormone tablet prescribed and adjusted by your provider.

2. Iron-Deficiency Anemia

What it is: A condition where the blood does not have enough healthy red blood cells to carry adequate oxygen to your tissues, usually because iron stores have run low.

Why it happens: Low iron intake, heavy menstrual periods, pregnancy, or slow blood loss from the gut can deplete iron over time. Even low iron stores without full-blown anemia can be enough to affect hair and energy.

Common symptoms: Fatigue that does not improve with rest, cold hands and feet, pale skin, shortness of breath on exertion, brittle nails, and increased hair shedding. Low iron is a well-recognized contributor to hair loss, especially in women.

Risk factors: Heavy periods, pregnancy, a vegetarian or vegan diet, frequent blood donation, and gut conditions such as celiac disease that affect absorption.

When to seek evaluation: A complete blood count (CBC) plus a ferritin test checks both for anemia and for low iron stores. This is a simple, low-cost test and iron levels are usually correctable with diet changes or supplements guided by a provider.

3. Other Nutritional Gaps (Vitamin B12, Vitamin D, and Zinc)

What it is: Low levels of specific vitamins and minerals that the body needs for energy production, nerve function, and healthy hair follicles.

Why it happens: Restrictive diets, limited sun exposure, older age, weight-loss surgery, and certain medications (such as long-term acid reducers) can lower vitamin B12, vitamin D, or zinc.

Common symptoms: Generalized fatigue and muscle weakness, tingling in the hands or feet with low B12, bone or muscle aches with low vitamin D, and hair shedding with low zinc or iron. Feeling cold is less specific here but can accompany the fatigue.

Risk factors: Vegans and vegetarians (B12 and zinc), older adults, people with limited sun exposure, and anyone with a gut condition that affects absorption.

When to seek evaluation: Blood tests can confirm these deficiencies. Do not start high-dose supplements on your own, since the right dose and duration depend on your levels and should be guided by a provider.

4. Not Eating Enough (Very Low-Calorie Dieting or Disordered Eating)

What it is: When the body runs on fewer calories than it needs for a sustained period, it slows the metabolism to conserve energy.

Why it happens: Aggressive dieting, skipping meals, an eating disorder, or simply undereating during a stressful stretch can leave the body short on fuel and on the protein and nutrients that hair and body heat depend on.

Common symptoms: Feeling cold much of the time, low energy, hair shedding, and often lightheadedness, low mood, or missed periods. The body lowers its internal thermostat and diverts resources away from non-essential tasks like growing hair.

Risk factors: A recent rapid weight loss, a very restrictive diet, high training loads without enough food, or a history of disordered eating.

When to seek evaluation: If you are undereating and struggling to stop, or you have lost weight without trying, talk to a provider. Disordered eating is a medical issue, not a willpower problem, and support is available and effective.

5. Chronic Stress and Recent Illness (Telogen Effluvium)

What it is: A temporary form of hair shedding that follows a physical or emotional shock, in which many hair follicles shift into a resting and shedding phase at once.

Why it happens: A high fever, an infection, surgery, childbirth, a crash diet, or a period of intense stress can trigger it. The shedding typically shows up two to three months after the event, which can make the cause hard to connect.

Common symptoms: Noticeably more hair coming out when you brush or wash, usually as overall thinning rather than bald patches. Fatigue and feeling run down often travel with the underlying stress or illness, though feeling cold is less typical for this cause alone.

Risk factors: A recent major life event, serious illness, new medication, or significant weight change in the previous few months.

When to seek evaluation: This form of shedding usually recovers on its own once the trigger passes. If the shedding is heavy, keeps going beyond about six months, or comes with the cold and fatigue described here, see a provider to check for thyroid or iron issues as well.

6. Less Common Causes (Pituitary and Other Autoimmune Conditions)

What it is: Occasionally the symptom trio traces to a problem in the pituitary gland (which signals the thyroid and other glands) or to another autoimmune or hormonal condition.

Why it happens: If the pituitary gland does not send enough signal, the thyroid and adrenal glands can underperform even when the thyroid itself is healthy. Other autoimmune conditions can cluster together with thyroid disease.

Common symptoms: A similar picture of fatigue, cold intolerance, and hair or skin changes, sometimes with low blood pressure, dizziness on standing, or changes in menstrual periods.

Risk factors: A history of a pituitary problem, head injury, radiation to the head, or another diagnosed autoimmune condition.

When to seek evaluation: These causes are uncommon but worth considering if standard thyroid and iron tests come back normal and symptoms persist. Your provider can order more specific hormone testing if needed.

When to Seek Medical Care

Emergency, call 911 or go to the nearest ER immediately if these symptoms occur with any of the following: chest pain or pressure, trouble breathing at rest, fainting or loss of consciousness, a rapid or irregular heartbeat, one-sided weakness or slurred speech, or new confusion or extreme drowsiness combined with very slow breathing and a body temperature below 95°F (35°C). Severe, long-untreated hypothyroidism can rarely progress to a dangerous state, and signs like a stroke or heart problem need care within minutes, so do not wait to see if it gets better.

If these symptoms come with thoughts of self-harm or suicide, this is also an emergency: call or text 988 (US) to reach the Suicide & Crisis Lifeline right away, or call 911 or go to the nearest emergency room if you or someone else is in immediate danger.

See a doctor soon (not necessarily an emergency) if the hair loss, feeling cold, and tiredness: have lasted more than a few weeks together; are getting worse; come with unexplained weight change, very heavy periods, or noticeable neck swelling; or are interfering with daily life. These patterns are easy to check with simple blood work, and most of the causes are treatable once identified.