Raynaud's phenomenon is a condition that affects blood flow to certain parts of the body, usually the fingers and toes. It occurs when small blood vessels constrict excessively in response to cold temperatures or stress, leading to color changes in the skin. Affected areas may turn white or blue and feel cold or numb. During a Raynaud's attack, blood flow returns as the body warms up, causing the skin to turn red and may feel tingly or painful. This condition can be primary, occurring on its own, or secondary, associated with other health issues like scleroderma or lupus.