Methylene chloride (MC) is used to remove the paint of bath tub for renovation. It is reported that 13 deaths occurred while using this. The main hazards stated are from inhalation and skin exposure and it is a carcinogen.
http://www.osha.gov/SLTC/methylenechloride/
Permissible exposure is 25 ppm (TLV-TWA) for 8 hr and 125 ppm (TLV-STEL) for 15 minute period
It is anaesthetic and inhalation can cause mental confusion, light-headedness, nausea, vomiting, headache. Continued exposure may cause increased light-headedness, staggering, unconsciousness, and even death. High vapor concentrations may also cause irritation of the eyes and respiratory tract. Exposure to MC may make the symptoms of angina (chest pains) worse. Skin exposure to liquid MC may cause irritation. If liquid MC remains on the skin, it may cause skin burns. Splashes of the liquid into the eyes may cause irritation.
Long-term (chronic) exposure: Studies on rats, mice indicate MC causes cancer.
OSHA interprets results to mean that there is suggestive (but not absolute) evidence that MC is a human carcinogen.
Generally bathrooms are small and the ventilation in it will be poor. While cleaning, it is likely that the doors also will be closed and persons working inside will be exposed to vapors.
One has to wear suitable respiratory protection and skin protection and someone must keep watch on the person doing the cleaning job.
Many chemicals used for cleaning jobs at home cause skin burns or atleast itching and not much awareness is seen in this aspect. I saw some books for home safety. But, every chemical can/container for home use shall have hazards and safety precautions printed in readable font size so that users can take care of themselves.