“Common side effects include headache, vomiting, confusion, shortness of breath, and high blood pressure. Other side effects include serotonin syndrome, red blood cell breakdown, and allergic reactions. Use often turns the urine, sweat, and stool blue to green in color.”
I’m pretty sure those are the side effects of ingestion/injection, not application to the skin. There are lots of things you can apply to your skin which would be bad to eat.
https://en.wikipedia.org/wiki/Methylene_blue
“Common side effects include headache, vomiting, confusion, shortness of breath, and high blood pressure. Other side effects include serotonin syndrome, red blood cell breakdown, and allergic reactions. Use often turns the urine, sweat, and stool blue to green in color.”
I’m pretty sure those are the side effects of ingestion/injection, not application to the skin. There are lots of things you can apply to your skin which would be bad to eat.