I've been looking at the data sheet for wd40 and your concern is not misplaced, it
may be harmful over long term, namely (and relevantly) skin irritation and dryness, inhalation hazard, and don't get it into the body. But having said that, these engineering safety sheets have a wide margin for safety, they tend to try and cover every eventuality and often go over-the-top somewhat to cover themselves legally.
I've always had a can of wd40 around, having a bicycle, having studied robotic engineering in college and when making prototypes, in fact I had some on my hands yesterday, and I never ever had sore airways or got skin irritation, even when the stuff got into little cuts on my hands.
Having said all that, I won't be making soap with it except for a test sample, the main reason being that wd40 tests at around PH 5 or 6 (it was hard to tell because it makes the test strip transparent), which won't like my alkali soap at all.
https://cdn.wd40company.eu/wd-40/en-GB/uploads/2018/01/22135513/WD-40-MULTI-USE-PRODUCT-AEROSOL.pdf
(the American data sheet is a lot easier to read than the UK one)
Thank you for bringing this information into the light of day but please consider that there should be data safety sheets for every household product, and many of those could indicate similar hazards. For example prescriptions and medications that have adverse health effects, hair products that are flammable or corrosive, and if you consider cosmetic make-up to be a skin medication it puts all the ingredients in a different light.
Common sense should always prevail.
