From the Manufacturer:
L-Histidine has been used in the treatment of ulcers as far back as the 1930's as it diminishes the acidity of the digestive juices. Half a teaspoon before a meals will reduce acidity in the stomach and allow for a more comfortable digestion.
L-Histidine also plays an important role in the proper health of our skin. It is the direct precursor of urocanic acid, a compound found in our skin tissue. Urocanic acid is one of the major UV light absorbing compounds found in our skin. Therefore, more L-histidine means better protection from the sun.
Histidine can be used in the treatment of dermatitis.