Can I use any soap or shampoo on my dreads? - Dreadlocks FAQ's
Of course you can....but let me recommend you stick to residue free soaps/shampoos and here are some reasons why:
Dreads start out as knots. As knots tighten they become dreads. Tightening occurs when knots are pressed together and friction prevents them from sliding apart. Residues act as a lubricant, reducing friction and the hair's ability to hold knots. This causes the knots to slip them apart which loosens the dread and prevents the dread from getting as tight as it otherwise could.
Residue free soaps get the hair cleaner and leave no lubrication behind. Because no residue is left to lubricate the hair, there is more friction and dreads lock much tighter and faster. This is one reason why using a residue free soap is a good idea.
Another reason is to avoid "dread rot".
Because the hair inside dreads is packed tightly together it has a tendency to trap everything the soap or shampoo leaves behind, thin layers of residue build up over time. As the residues build up, they coat the hair and lubricate it from the inside out. The residue coated dreads do not allow the air to circulate. This causes them to hold moisture for long periods of time which can eventually lead to mildew growing inside the dread. This mildew dies and rots inside your dreads and smells DEE-LIGHTFUL, like sack of wet towels that's been sitting in a warm gym locker for 3 months.