Hypothyroidism can also cause the body to retain more salt and water, contributing to weight gain.
The amount of weight gained varies. Some people experience only modest changes, while others notice a more substantial difference.
Importantly, thyroid-related weight gain is not always caused by increased body fat. Fluid retention can account for part of the change.
Severe or untreated hypothyroidism may produce more pronounced effects, but substantial weight gain should not automatically be attributed to the thyroid.
Weight loss associated with hyperthyroidism
Excess thyroid hormone can increase energy expenditure and accelerate the breakdown of fat and muscle.
As a result, a person may lose weight despite eating normally or even experiencing an increased appetite.
Other symptoms can include sweating, tremors, a racing heart, anxiety, frequent bowel movements, and difficulty sleeping.
Some individuals experience increased appetite without losing weight, particularly if food intake rises enough to offset the increased energy expenditure.
What should you do about unexplained weight changes?
If your weight changes significantly without an obvious explanation, consider a medical assessment.
Thyroid testing may be appropriate, especially when weight changes occur alongside other characteristic symptoms.
Avoid taking thyroid medication or supplements marketed as metabolism boosters without a confirmed diagnosis. Excess thyroid hormone can cause dangerous complications, including abnormal heart rhythms and bone loss.
The safest approach is to identify the underlying cause rather than trying to force the body to gain or lose weight.
3. Increased Sensitivity to Cold or Heat
The thyroid plays an important role in regulating energy use and heat production.
Consequently, people with thyroid dysfunction may notice changes in how they tolerate different temperatures.
Feeling unusually cold
People with hypothyroidism often feel cold when others are comfortable.
They may need extra layers of clothing, struggle in air-conditioned rooms, or experience persistently cold hands and feet.
Reduced metabolic activity can decrease heat production, while changes in circulation may contribute to discomfort.
However, cold intolerance can also occur with anemia, low body weight, poor circulation, and other medical conditions.
Feeling unusually hot
People with hyperthyroidism may feel excessively warm, sweat more than usual, and struggle in hot weather.
Excess thyroid hormone can increase metabolic activity and heat production. Some people experience warm, moist skin and an increased sensitivity to temperature.
These symptoms may occur alongside a rapid heartbeat, tremors, or unintended weight loss.
When is temperature sensitivity concerning?
Feeling cold or hot occasionally is normal. Persistent, unexplained changes are more significant, especially when several symptoms occur together.
If you develop unusual temperature sensitivity alongside fatigue, weight changes, menstrual irregularities, or palpitations, discuss the pattern with a healthcare professional.
A thyroid blood test can help determine whether abnormal hormone levels may be contributing.
4. Hair Thinning, Hair Loss, and Changes in Skin
Thyroid hormones influence the normal growth cycle of hair follicles and contribute to healthy skin function.
Both hypothyroidism and hyperthyroidism can affect hair growth, although the pattern and severity vary.
Hair changes associated with hypothyroidism
People with an underactive thyroid may notice dry, coarse, brittle hair or diffuse thinning across the scalp.
Some also experience thinning of the outer portion of the eyebrows.
Hair growth may slow, and the skin may become dry or rough.
These changes can develop gradually, making them easy to attribute to aging, stress, or hair treatments.
Hair changes associated with hyperthyroidism
Excess thyroid hormone can also disrupt the hair growth cycle.
Some people develop diffuse hair shedding or notice that their hair becomes finer.
The hair loss may become apparent several months after the underlying hormonal disturbance begins.
What about skin changes?
Hypothyroidism may cause dry, rough, or cool skin. In more pronounced cases, fluid accumulation in tissues can produce puffiness, particularly around the face.
Hyperthyroidism may cause warm, moist skin because of increased heat production and sweating.
Certain thyroid-related autoimmune conditions can also affect the skin directly, although these manifestations are less common.
Other possible causes
Hair loss is not specific to thyroid disease.
Iron deficiency, recent illness, childbirth, significant stress, nutritional deficiencies, certain medications, and genetic hair loss can all contribute.
If hair loss is sudden, severe, patchy, or accompanied by other symptoms, seek medical advice rather than immediately assuming a thyroid problem.
Depending on your history, a clinician may assess thyroid function and consider other causes of hair loss.
5. Menstrual Irregularities and Fertility Problems
Thyroid hormones interact with the reproductive system and can influence menstrual function, ovulation, and fertility.