Why does our face become reddish in the sun?

The reddening of our face when exposed to the sun is primarily due to the expansion of blood capillaries. The process involves a complex series of physiological reactions that occur as a response to the sun's rays. Let's discuss the factors contributing to this phenomenon in detail:

1. Expansion of blood capillaries:
When our face is exposed to the sun, the blood vessels near the surface of the skin dilate or expand. This expansion is a natural response to regulate body temperature and maintain homeostasis. The dilation of blood capillaries allows more blood to flow to the surface of the skin, increasing blood circulation in that area. As a result, the skin appears reddish or flushed.

2. Effect of light:
Sunlight consists of various wavelengths, including ultraviolet (UV) rays. Exposure to UV rays triggers a response in the skin, leading to the dilation of blood vessels. This dilation is caused by the release of certain chemicals, such as nitric oxide, which are stimulated by UV rays. The increased blood flow to the skin helps dissipate heat and prevent overheating.

3. Break up of red blood cells (RBCs) and release of hemoglobin:
Contrary to popular belief, the reddening of the face in the sun is not primarily caused by the break up of red blood cells and the release of hemoglobin. While sunlight can cause some damage to RBCs, the amount is generally minimal and not significant enough to cause visible redness in the skin.

4. Irritation of the skin:
Sun exposure can also cause irritation to the skin, especially in individuals with sensitive skin or certain skin conditions. This irritation can lead to redness, but it is not the main cause of the reddening of the face in the sun.

In conclusion, the reddening of our face in the sun is primarily due to the expansion of blood capillaries near the skin's surface. The dilation of these blood vessels is a natural physiological response to regulate body temperature and maintain homeostasis. Factors such as the effect of light and skin irritation can also contribute to the overall redness, but they are secondary to the dilation of blood capillaries.

Answer is b)expansion of blood capillaries