What substances circulate through the body to provide nourishment to the skin?

Blood and lymph are the primary substances that circulate through the body to provide nourishment to the skin. Blood carries essential nutrients, oxygen, and hormones to the skin cells, facilitating growth, repair, and overall skin health. It also helps in the removal of waste products from cellular metabolism.

Lymph, on the other hand, is a fluid that is part of the lymphatic system and is vital for immune function. It also transports absorbed fats from the digestive system and assists in the removal of toxins and waste. This dual role of providing nutrient-rich fluid and facilitating waste removal is critical for maintaining the health and appearance of the skin.

While oxygen is essential for skin health and is transported in the blood, it is the blood as a whole that serves as the primary system for delivering nutrients. Carbon dioxide is a waste product that is not nourishing. Hormones and enzymes play supportive roles but do not directly nourish the skin. Similarly, while proteins and minerals are important for skin structure and function, they are ultimately delivered to the skin via the blood. Therefore, blood and lymph are the correct and most relevant choices in this context.