Hypothyroidism changes how you look, feel, and function in ways that can be subtle at first and increasingly obvious over time. The most visible signs are dry, scaly skin, a puffy face (especially around the eyes), thinning hair, and a general appearance of fatigue or sluggishness. But the condition also produces a constellation of internal changes that affect your weight, body temperature, heart rate, and mental sharpness.
Skin, Hair, and Nail Changes
The most common visible sign of hypothyroidism is excessively dry, scaly skin, particularly on the shins, forearms, palms, and soles. In a study of 460 hypothyroid patients, 57% had this kind of skin dryness, making it the single most frequent dermatological finding. The skin can also take on a pale or slightly yellowish tint. That yellowish color comes from a buildup of carotene in the skin, which happens because the body processes it more slowly when thyroid hormones are low.
Hair changes are the second most noticeable feature. Nearly half of patients in the same study had diffuse hair loss, and about 30% developed coarse, brittle scalp hair. One of the more distinctive signs is loss of the outer third of the eyebrows, a pattern specific enough that clinicians use it as a visual clue during exams. Eyelashes can thin as well. Nails often become brittle, ridged, and slow-growing.
The most classic skin finding is called myxedema: a type of swelling that looks puffy but doesn’t leave an indent when you press on it. The skin feels doughy, waxy, and thickened. It shows up most prominently around the eyes, on the shins, and on the hands and feet.
Facial Puffiness and Expression
A swollen, puffy face is one of the hallmarks of hypothyroidism and one of the reasons people search for what the condition “looks like.” About 29% of patients develop noticeable facial edema. The puffiness concentrates around the eyes, giving the eyelids a heavy, swollen appearance. This swelling differs from allergic reactions or fluid retention from other causes because it doesn’t pit when pressed.
Over time, untreated hypothyroidism can create a characteristic “dull” facial expression. The features appear thickened, the face looks rounded, and the overall impression is one of lethargy. The tongue can enlarge slightly, and the voice may become deeper or hoarse as the vocal cords thicken.
Weight Gain and Body Shape
Weight gain is probably the most widely associated sign of hypothyroidism, but the reality is more nuanced than most people expect. Thyroid hormones regulate your basal metabolic rate, how you burn fat, and how your body generates heat. When those hormones drop, your metabolism slows, and your body burns fewer calories at rest.
That said, the actual weight gain directly caused by hypothyroidism is typically modest. Much of it comes from fluid retention and the swelling (myxedema) rather than fat accumulation. Treatment with thyroid hormone replacement generally produces only modest weight loss, and not in every patient. If you’ve gained a significant amount of weight, other factors are likely contributing alongside the thyroid dysfunction.
Feeling Cold All the Time
Cold intolerance is one of the earliest and most persistent symptoms. Your thyroid controls heat production through two mechanisms: your baseline metabolic rate and your body’s ability to ramp up heat generation in response to cold environments. Both are impaired in hypothyroidism.
Research comparing hypothyroid patients on standard thyroid medication to healthy controls found that even with treatment, patients maintained lower temperatures in their hands and feet. The medication replaces thyroid hormone at a steady dose but can’t dynamically adjust the way a healthy thyroid would, leaving the body less responsive to cold exposure. This is why many people with well-managed hypothyroidism still complain of cold hands, cold feet, and a general sensitivity to chilly environments that other people tolerate easily.
Brain Fog and Mood Changes
Hypothyroidism doesn’t just change how you look. It changes how you think. The term “brain fog” comes up constantly among patients, and research into what that actually means reveals a specific cluster of symptoms. In surveys, more than 95% of hypothyroid patients associated brain fog with low energy and fatigue, forgetfulness, sleepiness, and difficulty focusing.
The cognitive effects go deeper than general tiredness. Patients describe struggling to find the right words, losing the ability to follow what they’re reading, and having trouble making decisions. Some people report that watching a screen or reading a book becomes an effortful task rather than something automatic. Depressed mood and anxiety also appear alongside these cognitive symptoms, though fatigue and memory problems are more prominent than mood disturbances for most people.
A Slower Heart and Less Energy
Thyroid hormones directly influence heart rate and the force of each heartbeat. In hypothyroidism, the heart rate drops and each beat pumps less blood. The result is a state of lower cardiac output that contributes to fatigue, exercise intolerance, and sometimes shortness of breath with activities that previously felt easy. In severe or prolonged cases, this reduced cardiac function can contribute to heart failure.
Constipation, muscle aches, and joint stiffness round out the picture. The digestive system slows alongside everything else, and muscles can feel heavy, weak, or cramped.
Neck Swelling From an Enlarged Thyroid
Some people with hypothyroidism develop a visibly enlarged thyroid gland, known as a goiter. A normal thyroid weighs 10 to 20 grams and sits low in the front of the neck. When it enlarges, it grows forward because the muscles and skin in front of it offer little resistance. A goiter can be subtle, visible only when you swallow, or large enough to be obvious at rest. Not everyone with hypothyroidism develops one, and the size doesn’t necessarily correlate with how severe the hormone deficiency is.
What It Looks Like in Infants
Congenital hypothyroidism, present at birth, has its own set of visible signs. Early on, newborns may appear unusually sleepy and floppy, have trouble feeding, and develop jaundice that lasts longer than expected. Their cry may sound weak or hoarse.
If the condition isn’t caught by newborn screening and goes untreated for the first six weeks, more obvious physical features develop: a flattened nasal bridge, puffy eyelids, a large tongue that may protrude from the mouth, coarse hair, thick and dry skin that feels cool to the touch, and a distended abdomen often with an umbilical hernia. These late signs are now rare in countries with routine newborn screening programs, but they illustrate how profoundly thyroid hormones shape normal development.
When Hypothyroidism Becomes Dangerous
At its most extreme, untreated hypothyroidism can progress to a medical emergency called myxedema coma. Despite the name, you don’t have to be fully unconscious. The hallmarks are confusion or disorientation, dangerously low body temperature, slow breathing, a very slow heart rate, low blood pressure, and significant swelling. Organs begin to shut down, and without emergency treatment, it can lead to respiratory failure or death. This is rare and typically occurs in people with long-standing, untreated disease who experience an additional stress like an infection or surgery.