Co-washing is short for conditioner washing, meaning you skip the shampoo and cleanse your hair using a conditioner only.
Many shampoos contain sulfates which can leave your hair dry and prone to breakage due to stripping natural oils and moisture from the strands of your hair. By cutting out shampoo, your hair is better able to maintain its natural moisture levels and can therefore stay stronger and healthier.
The way to co-wash is by wetting your hair, then taking a small amount of conditioner and massaging your scalp, rubbing gently using your fingertips. This should help loosen any dirt and residue, whilst keeping naturally beneficial oils. You then saturate your hair with the conditioner, spreading it throughout the length of your hair, finger combing (or using a wide-tooth comb) to carefully remove any tangles.
However, you should still use a clarifying shampoo every two to four weeks to help get rid of build-up. The purpose of a clarifying shampoo is to deep clean your hair from dirt and oil that accumulates on your scalp.