In v13 and OS X 10.x, certain font types do not support the italic typeface using static text. If the text requires italics while using static text, only use the official fonts listed by Apple:

- Arial
- Courier
- Georgia
- Helvetica
- Hoefler Text
- Palatino
- Times
- Trebuchet MS
- Verdana

https://support.apple.com/kb/ta20744