Mantra for beautiful skin in Hinduism is associated with Goddess Mahagauri or Goddess Parvati. The mantra should be chanted 108 times early morning just before sunrise after taking bath.
Mantra For Beautiful Skin
त्रैलोक्यमंगल
त्वंहि तापत्रय हारिणीम्।
वददं चैतन्यमयी महागौरी
प्रणमाम्यहम्॥
The person chanting the mantra should have a clean mind and clean body. The mantra should be chanted with utmost devotion.
A lamp should be lit using pure cow ghee and the person chanting the mantra should sit facing east or northeast.
Please note that skin is a perishable part and it will undergo change. So be careful about what you are demanding through the mantra. Instead of focusing on perishable things one should use the time to gain real that will last forever and help us when we are lonely and confused in life.