Is there an expiration date for unused/unopened hair dye?
If the hair dye is unopened, it can be used within 3 years from the manufacturing date.
The product is good for use within 3 years from its manufacturing date if it is still unopened. The product may not work as well after the 3 year mark.
Can the leftover hair color/bleach mixture be kept and reused?
The remaining mixture cannot be kept.
The chemical mixture for either bleach or hair dye cannot be stored once the components have been combined (i.e. the dye and developer). Please ensure that the remaining mixture is washed off and discarded immediately.
Over time, the mixture not only decreases in dyeing power, but also produces gas which may use pressure buildup in the sealed container. This is extremely dangerous as it may cause an explosion.
How long does it take before the opened hair dye expires?
It varies depending on the type of hair dye.
For products that come in a tube and in 2 solutions (i.e. the dye and developer respectively), they can be used within 3 months. The color of chemicals may change, but rest assured that it will not affect the dyeing process.
For aerosol products, hair manicures, color treatments and color rinses, do use them within 6 months once opened.
For products where Solution 1 (i.e. the dye) comes in a bottle or is a liquid, it cannot be kept as air has already entered the container after opening.