Final answer:
The first phase of tanning, involving the rapid darkening of melanin when exposed to UVR, is known as Immediate Pigment Darkening (IPD). This process is a defense mechanism of the skin to protect deeper tissues from UV damage, although it is temporary and repeated exposure can increase skin cancer risks.
Step-by-step explanation:
The first phase of tanning is referred to as Immediate Pigment Darkening (IPD), or sometimes Immediate Tanning Response. This phase involves the rapid darkening of melanin that is already present in the skin being exposed to Ultraviolet Radiation (UVR). This immediate darkening is part of the skin's defense mechanism which helps to block UV penetration and prevent damage to the vulnerable skin tissue deeper down.
Sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes, leading to the production and accumulation of melanin in inert skin layers to absorb future exposures and protect the living cells beneath from UV-B radiation, which can excite DNA molecules, distort the DNA helix, potentially leading to mutations and the formation of cancerous cells. It is important to note that the effects of tanning and melanin production are impermanent as melanin-filled keratinocytes eventually slough off.
While a tan might provide temporary protection, repeated exposure to UVR can increase the risk of skin cancer, emphasizing the importance of using sun protection products with an effective Sun Protection Factor (SPF) to mitigate these risks.