Magnesium Ascorbyl Phosphate is a stable, water soluble derivative of Vitamin C (L-Ascorbic acid mono-dihydrogen phosphate magnesium salt). Unlike L-Ascorbic Acid, it does not readily degrade in formulas containing water.  It is considered light-stable and oxygen-stable. Studies of MAP in aqueous solutions indicate it retains over 95% of its potency at 40°C without any pH adjustment.
By inhibiting tyrosinase activity, MAP is capable of suppressing skin pigmentation, making it effective in whitening dark skin, or areas of dark skin.  It should be noted, one study indicated it might be needed at a concentration of 10% to be effective at inhibiting melanin production1.
Unlike Ascorbyl Palmitate, Magnesium Ascorbyl Phosphate (MAP) appears to have the same potential to boost skin collagen synthesis as does Ascorbic Acid, but at lower concentrations. For those with sensitive skin or those wanting to avoid the exfoliating effects of highly acidic Ascorbic Acid, MAP may be the preferred choice.
Applications
Suncare and after-sun products
Makeup products
Skin lightening products
Anti aging products
Creams and lotions
This is a cosmetic raw material and is meant for external use only.
Magnesium Ascorbyl Phosphate (MAP) may discolor in formulations with a pH below 6, so is best used in products with a final formulation pH between 6.0 - 7.0.
The solubility of MAP in water is 154g/l at 25C/77F (that's at most 15.4%)
MAP is stable at 80C/176F for up to 20 hours; this means that it should withstand heating to this temperature for short periods in formulations without a problem.  Therefore, it can be added to the water phase prior to heating.
You can also predisperse it in a small amount of distilled water and add at the end of the formulation process.
If you're having trouble dissolving MAP in water, warming the solution to about 40°C (104°F) will help.

Typical usage rate:  0.2 - 3%, up to 10%
Appearance:  White to off-white powder with a mild odor 

INCI: Magnesium Ascorbyl Phosphate