Retriderm Vitamin A Serum EXTRA 1ozRetriderm Vitamin A Serum EXTRA delivers .75% of retinol to the skin. Retriderm Vitamin A Serum EXTRA is perfect for you if you have some aging skin concerns. Retriderm Vitamin A Serum EXTRA can also be used after you have completed a regimen of Retriderm Vitamin A Serum or if you have more advanced photoaging damage to your skin.