Final report of the safety assessment of L-ascorbic acid, calcium ascorbate, magnesium ascorbate, magnesium ascorbyl phosphate, sodium ascorbate, and sodium ascorbyl phosphate as used in cosmetics 

In 2005 researchers reviewed evidence on the safety and tolerability of ingested and topical use of commercially available ascorbic acid preparations. Given the widespread use in cosmetics, authors assessed preclinical evidence relating to L-ascorbic acid, calcium ascorbate, magnesium ascorbate, magnesium ascorbyl phosphate, sodium ascorbate and sodium ascorbyl phosphate. Helps guide industrial selection of ascorbic acid salts depending on use. 

References:

Elmore A. R. (2005). Final report of the safety assessment of L-Ascorbic Acid, Calcium Ascorbate, Magnesium Ascorbate, Magnesium Ascorbyl Phosphate, Sodium Ascorbate, and Sodium Ascorbyl Phosphate as used in cosmetics. International journal of toxicology, 24 Suppl 2, 51–111. https://doi.org/10.1080/10915810590953851