Final answer:
Skin redness following a sunburn is due to the inflammation response of the body, leading to increased blood flow and the arrival of immune cells at the site of damage.
Step-by-step explanation:
Your skin remains red after a bad sunburn primarily because of inflammation, which leads to increased blood flow to the affected area. When the skin is damaged by excessive UV light exposure, inflammatory chemicals are released, causing nearby blood vessels to dilate. This increased blood flow brings various immune cells to the site to aid in healing, but it also results in the redness and warmth associated with sunburn. Over time, other processes including the production of pigments may occur to further protect your skin. Blisters, if formed, also indicate damage to the skin's deeper layers, including the epidermis and possibly the dermis.