What role does TSH play in allergy?

TSH (thyroid-stimulating hormone) is secreted by the pituitary gland and regulates thyroid function. A direct role in allergy is not clearly established. However, thyroid hormones can modulate the immune system: hypothyroidism (elevated TSH) is associated with a heightened Th2 response, which may promote allergic reactions. Conversely, some studies suggest TSH itself may act on immune cells like mast cells and promote histamine release – but this is largely mechanistic and not confirmed by robust human clinical trials. In practice, TSH is measured to assess thyroid status, not for allergy diagnosis. An abnormal TSH may indicate thyroid disease, which can cause symptoms (fatigue, skin changes) that mimic allergies. Caveat: TSH alone is not an allergy marker; specific IgE tests or skin prick tests are needed for allergy evaluation. The evidence for a direct TSH–allergy link is weak and primarily mechanistic.