Because grout is porous and this is a damp climate – and yes, in most cases it can be restored without regrouting. Grout absorbs moisture, soap film, and body oils, which feed the discoloration and mildew you’re seeing along shower joints and floor lines.
Moisture control is the underlying fix. The Oregon Health Authority advises keeping indoor humidity between 30 and 60 percent and running exhaust fans to vent shower and laundry moisture outside; the EPA’s mold guidance targets the tighter 30-50 percent band. From October through May, plenty of Willamette Valley bathrooms sit well above that – especially in older Corvallis and Albany housing stock with undersized or ducted-to-nowhere exhaust fans.
Professional cleaning uses high-pressure hot water extraction to pull soil out of the grout pores rather than smearing it around the way mop-and-bucket cleaning does. We finish by sealing the grout, which slows reabsorption and buys you considerably longer between cleanings. If grout is cracked, missing, or the discoloration is under a failing seal rather than in the pores, we’ll say so – sealing won’t fix that.