“Bleach is generally not recommended because it only removes surface mould, which is ineffective for porous surfaces like grout as the mould roots itself deeply.
“Also, bear in mind that some bleaches can fade the colour of your grout.
“The trick to cleaning this area is to work in small sections and use a stiff toothbrush to really work your cleaner of choice into the mouldy shower grout.
“Let it develop for at least 30 minutes, then rinse, repeat as necessary, and dry. Don’t forget to keep the bathroom ventilated while you work!”
READ MORE: Method to brighten stubborn tile grout stains in five minutes
source: express.co.uk