What is the difference between serum and cream? Why do you need both?

A serum is a thinner consistency than a cream. When layering products (which is the concept of most skin care regimes) we always advise to go from thin to thick and wait a minute between application. 

aliangé's 2 + 2 concept in aliange is exactly this. In the morning use two protective products and in the evening use two repairing products.

They have different ingredients but are synergistic in creating your ultimate beautiful skin. If skin is sensitive we recommend build up the nightly products slowly - either alternating them initially or building up to the nightly application of the retinol before adding in the serum first.