Which of the following is not a common cause of surface stains on nails?

Surface stains on nails can result from various external factors that come into direct contact with the nail plate. Smoking introduces tar and nicotine that can stain nails, while food dyes can also contribute to discoloration, especially when hands and nails come into contact with highly pigmented foods. Nail polish, on the other hand, can leave stains on the nails if not removed properly, particularly if the polish contains certain dyes or if the nails are not protected with a base coat.

In contrast, poor blood circulation affects the overall health and coloration of the nails but does not specifically lead to surface stains. Surface stains are generally a result of exposure to substances or materials that physically alter the color of the nail, rather than systemic health issues like circulation problems. Thus, understanding the distinction between external stain-causing agents and internal health conditions helps identify the correct answer regarding the common causes of nail surface stains.