Ingredients: why should they be applied immediately after mixing?
The reason the ingredients come in different bottles is that, once mixed together, a chemical reaction occurs.
If you keep the mixture in the “squashy bottle”, without breaking the seal, the chemical reaction between the colorant and the developer continues.
If this chemical reaction is not stopped by applying the mixture to your hair, oxygen is released. The mixture swells, the bottle can bust and cause the colouring product to spray everywhere.
As rule, always follow the instructions found on every Garnier hair colouring product.