The general rule of thumb is to let semi-permanent dye sit for 20-45 minutes, depending on the type of dye and your hair's natural porosity. This may seem like a long time, but trust us, it's worth the wait - just like baking a cake, you need to let the ingredients work their magic. During this time, the dye is penetrating your hair shaft, depositing color and moisture.
It's essential to note that overprocessing can lead to dry, brittle hair and a faded color. Imagine leaving your favorite book outside on a rainy day - it's not going to end well. To avoid this, make sure to follow the instructions carefully and keep an eye on the time. If you're unsure, it's always better to err on the side of caution and rinse the dye out a bit sooner.
Perfect Hair Color Timing: How Long Should You Let It Sit? | ShunSalon
A good way to think about it is to compare it to working out - you need to find the right balance to get the best results. If you don't exercise enough, you won't see any progress, but if you overdo it, you might end up injured. The same applies to semi-permanent dye - you need to find the sweet spot to achieve the perfect color.
