If you have a thyroid problem that is not treated properly, serious health problems can result.

An overactive thyroid (hyperthyroid) can lead to a number of problems including:

• eye problems, such as bulging eyes, blurred or double vision or even vision loss
• heart problems, such as rapid heart rate, problems with heart rhythm or heart failure — these problems can usually be treated
• brittle bones (osteoporosis)
• red, swollen skin — occurring particularly on the shins and feet
• thyrotoxic crisis, which is a worsening of symptoms causing fever, rapid heart rate and delirium — this requires urgent medical attention

An underactive thyroid (hypothyroid) can cause a range of complications, including:

• an enlarged thyroid, or goitre, which may cause problems with swallowing and breathing
• high cholesterol and associated heart disease
• nerve damage causing tingling, numbness and pain in the legs, arms or other affected areas
• infertility
• birth defects
• miscarriage or premature birth
• mental health issues such as depression
• myxedema, which is a rare, life-threatening condition involving intense cold intolerance, lethargy and drowsiness that can lead to unconsciousness — myxedema requires urgent medical attention