Because Meg told him he would be fine, he believed it. He assumed it as truth and would accept that. After all, she had no earthly reason to lie to him. And because she'd done so well to take care of him so far, he didn't think she'd stop simply because he was in a current state of being unwell.
He had no idea what vapo rub was like, what it did or the texture and smell of it, so he watched her carefully, her various expressions when it came to the item in question. He was glad he'd wore a simple shirt that could be taken off and discarded without any issue, because anything more complicated involving buttons and he would have probably told her it wasn't necessary. He hadn't needed the help in getting his shirt off, in fact he made a point of saying, "I could have removed my shirt myself, Meg." as she'd been pulling it off of him. It'd been muffled by the act, but the point got across all the same. He noted the scrutiny of her gaze on his body and it made him curious as to what she thought. He was proud of this vessel, although, now it was his body. Not his vessel.
"It smells funny and feels odd against my skin. Is this truly supposed to make me able to breath easier?" He wasn't skeptical, but he wondered how something applied to his skin would allow him the ease of breathing. That was, until he began to take in more breaths as she continued to spread the substance across his skin. It was odd, but even between the smell and the fact he was sick, he was aware that Meg had never touched him in this manner before. It was probably for the best that his skin was already flushed because of his current ailment.