LEVEL 4
UV and Photoaging Science
UV damage goes beyond the visible "sunburn." It silently erodes the skin through immune suppression and DNA-level damage. Here, we explain the mechanisms of photoimmune suppression and DNA damage repair in detail.
The epidermis contains immune cells called Langerhans cells that serve as "sentinels," recognizing foreign substances and pathogens to initiate immune responses. Upon UV exposure (especially UVB), the number and function of Langerhans cells decrease significantly, suppressing local skin immunity.
This "photoimmune suppression" not only makes the skin more susceptible to infections but also reduces its ability to eliminate abnormal cells (pre-cancerous cells). This is one factor contributing to the increased risk of skin cancer from UV exposure.
There are two main types of UV-induced DNA damage.
CPD (Cyclobutane Pyrimidine Dimer): Adjacent pyrimidine bases (thymine or cytosine) form a cyclobutane ring bond. This is the most commonly generated type after UVB exposure, accounting for approximately 75% of all DNA damage.
6-4PP (6-4 Photoproduct): A covalent bond forms between positions 6 and 4 of adjacent pyrimidine bases. Less common than CPD but causes greater distortion of the DNA double helix structure.
Human cells have mechanisms to repair UV-induced DNA damage. The most important is the NER (Nucleotide Excision Repair) pathway. NER recognizes the damaged site, excises a fragment of approximately 25-30 nucleotides containing the damage, and re-synthesizes it with the correct sequence.
However, this repair is not perfect. When repair oversights and errors accumulate, mutations arise. Mutations in the p53 gene (a tumor suppressor gene) in particular significantly increase the risk of developing skin cancer.
Reactive oxygen species (ROS) generated by UV radiation oxidize the guanine base in DNA, producing 8-OHdG (8-hydroxy-2'-deoxyguanosine). 8-OHdG is a representative biomarker of oxidative DNA damage, and its accumulation serves as an indicator of carcinogenesis risk.
In addition to physical UV blocking with sunscreen, incorporating Vitamin C (ascorbic acid) and Vitamin E (tocopherol) and other antioxidant ingredients into your skincare routine is an effective preventive approach that suppresses ROS generation and reduces DNA damage.
Understanding the "invisible damage" of UV rays provides scientific rationale for the importance of applying sunscreen every day.
KAIAN develops skincare products based on photoaging research.
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