The thyroid is a gland in the neck. It makes thyroid hormone. A hormone is a chemical messenger for the body. If there is a problem with the thyroid, the level of thyroid hormone may change. This can lead to symptoms.

Hypothyroidism

With this problem, your thyroid gland doesn’t make enough hormone. The most common cause of hypothyroidism is Hashimoto thyroiditis. This occurs when the body’s immune system attacks the thyroid gland. Hypothyroidism may also occur if there’s a severe deficiency of  iodine in the body. The thyroid needs iodine to make hormone. Problems with the pituitary gland can lead to inadequate production of thyroid hormone. If the thyroid gland is removed during surgery, hypothyroidism will result.

Common symptoms

These are some of the most common symptoms:

• Low energy, fatigue, depression
• Feeling cold
• Muscle pain
• Slowed thinking       
• Constipation
• Heavier menstrual periods with prolonged bleeding 
• Weight gain
• Dry and brittle skin, hair, nails
• Excessive sleepiness

Hyperthyroidism

With this problem, the thyroid gland produces too much hormone. The most common cause is Graves disease. This is due to the body’s immune system telling the thyroid to make too much hormone. Another cause is a nodule (small bump) in the thyroid gland. This can cause hyperthyroidism if the cells in the nodule produce more hormone than the rest of the gland.

Common symptoms

These are some of the most common symptoms:

• Shaking, nervousness, irritability
• Feeling hot
• A rapid, irregular heartbeat
• Muscle weakness, fatigue
• More frequent bowel movements
• Shorter, lighter menstrual periods
• Weight loss
• Hair loss
• Bulging eyes

Nodules

Nodules are lumps of tissue in the thyroid gland. Most often, the cause of nodules isn’t known. But they may be more common in people who’ve had medical radiation to the head or neck. Sometimes they can be felt on the outside of the neck. Most of the time, nodules don’t affect the production of thyroid hormone. They usually cause no symptoms. Most nodules are noncancerous. But sometimes a nodule may be cancerous.