The lack of light in the bathroom would not directly cause the mold growth.
Mold in bathroom ceiling and walls.
If that s outside of your budget you can install a timer switch on the existing fan.
Grime from body oils and soap scum which is washed off and onto the shower or tub create a food source for mold to feed on.
Bathroom mold occurs primarily because mold loves damp dark isolated spaces says larry vetter of vetter environmental services in smithtown n y.
Cleansers with bleach or even white vinegar can often keep the slimy hairy growths from taking root in the bathroom.
And of course there are abundant water sources for mold created by the running water and steam.
Squeegee shower walls and glass doors after every use to help remove the moisture that encourages the growth of mold on your walls and also prevent unsightly hard water and soap scum buildup.
Liberally apply on painted walls.
Mold and mildew resistant paints are naturally designed to prevent mold and mildew from growing in the house.
The main cause of mold on a bathroom ceiling is a broken or ineffective exhaust fan.
Nothing beats this practical solution to mold in the bathroom ceiling.
Combine two tablespoons of borax with 1 4 cup white vinegar and two cups of hot water in a bowl.
Pour into a spray bottle.
Here is a link.
Typically a bathtub shower or entire bathroom remains damp enough for mold growth just from showering or bathing common causes of bathroom mold.
Wearing gloves and a mask can protect people from inhaling any mold spores as.
If you apply the mold resistant paint to the ceiling you already have a fool proof solution to mold problems in that region of your bathroom.
Removing mold from painted or wallpapered walls.