What Can Cause Pimple With White Puss?

good evening doctor i m karthik from maldives and 27yrs old my question is regarding pimples... when i was 20's i got pimple but now also i got two days back on my upper lips with small white pus, y is it like that? is there any problem in diet? what should i do to avoid? can u give some suggestions and reason doctor.