While henna is a good alternative for conventional hair dyes, it still has disadvantages. Nothing’s perfect, after all. Below are the cons of using henna as hair dye: 1. Henna takes time to develop Patience is a virtue when it comes to dyeing your hair with henna. Unlike traditional hair dyes, which take about an hour to develop, henna will take you about 1 to 6 hours. 2. It can get messy Henna has a muddy texture, so the application can be messy.