National Vitamin C Day is observed annually on April 4 to highlight the health benefits of vitamin C and the dangers of its deficiency. This day celebrates the essential role of vitamin C, also known as ascorbic acid, in immune function, collagen synthesis, and tissue repair, while also acknowledging its antioxidant properties. The holiday was launched by SkinCeuticals, a skincare brand founded by dermatologist Sheldon Pinnel, to promote the benefits of vitamin C in skincare. Celebrations may include consuming vitamin C-rich foods, such as citrus fruits and bell peppers, and incorporating vitamin C serums into skincare routines. The history of vitamin C dates back to the 15th century when the ability of citrus fruits to prevent scurvy was recognized, with significant contributions to its study made by James Lind in the 18th century and Albert Szent-Györgyi in the 20th century.