Hashimoto’s thyroiditis is an autoimmune condition: the immune system produces antibodies that target the thyroid gland. Over time, that ongoing inflammation can reduce how much thyroid hormone the gland makes, leading to hypothyroidism. Because thyroid hormone sets the pace for nearly every cell, the effects show up everywhere — energy, weight, mood, digestion, skin, hair, cycles, and how cold you feel.
Hashimoto’s often develops slowly. Antibodies can be elevated for years while TSH still reads “normal,” which is why so many people feel unwell long before they’re diagnosed. It’s also more common in women and tends to run in families.