How to make the Skin Strong to fight against UV

The skin strong against UV is dark skin becoming darker instead of red when exposed to sunlight. The skin weak against UV is fair skin becoming red when exposed to sunlight. The reason that the skin becomes red is that DNA of the skin is damaged.
 
The method that the person who is easily affected by UV changes to the person who is strong against UV is soaking in bathtub.
 
Heat shock protein that is a protein increasing by the stimulation of heat. Usually heat shock protein increases when the cells are damaged by bacterial infection or others and repairs the damaged cells. The increase of heat shock protein elevates the ability to repair the damaged skin cells. Therefore, the skin becomes strong against UV.
 
The easiest way to increase heat shock protein is soaking in a bathtub once in three days.
If you soak in a bathtub every day, your body gets used to the heat stimulation and heat shock protein doesn’t increase easily. Also the amount of heat shock protein is peak 2 days after soaking in a bathtub and returns to the original amount in 7 days. So 3 days later when heat shock protein starts to decrease is a good timing to stimulate again by soaking in a bathtub to keep sufficient amount of heat shock protein in the body.
 
Soaking in water of 41 degrees C (105.8 degrees F) for 15 minutes once in 3 days is effective to increase heat shock protein. Taking a shower on other 2 days with water of 37 degrees C is recommended not to get used to water of 41 degrees C.
 
The female B whose photoaging is progressed tried the above bathing method for 2 weeks.
The important points at the time of bathing are taking water, taking rest outside of the bathtub when it feels hot and sweating on the face that is the proof that heat shock protein increases.
As the result of the 2 weeks trial of the bathing, her skin became strong against UV as shown in the comparison between the before and after the test of exposure to weak UV for 1 minute (Fig. 2). Also heat shock protein in her blood increased by 1.3 times.