The penetrating heat action of Cura-Heat lasts for 12 hours and once removed pain relief can continue for a further 12 hours, resulting in up to 24 hours pain relief.These heat pads provide targeted, warming relief from minor muscular and joint aches and pains. The heat packs can be attached to clothing if needed, heat then radiates through to the source of pain, which increases circulation and relieves sore and stiff muscles.Cura-Heat contains iron, carbon and water, and when in contact with oxygen, heat is produced. The Heat then increases blood flow to the painful area, which helps to reduce pain, decreases stiffness, and relaxes sore muscles.If symptoms persist or worsen, seek medical advice. For external and single use only.