Been wearing cycling cap under helmet since I started riding in the early 1970s. Wash that when it looks dirty.
About every 6 months I throroughly scrub helmet straps; replace foam pads as necessary.
Disgustingly HOT in Philly?
Heck, here in AZ we had 72 days so far of over 100 degrees this year.
Hottest I've commuted in in Tucson was 117 degrees.
Wanna trade temps?