Can i apply mometasone 0.1% cream straight to my perioral dermatitis or does there have to be a delivery agent like cetaphil mixed with it?

Depends: Do you know why you have dermatitis. If could be allergy, but it could also be nutritional deficiency. Try taking multivitamins for at least a couple of weeks to see if that relieves the symptoms. Have a healthy diet, exercise 30 minutes/day, drink plenty of water, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV vaccine

Absolutely NOT!!: The most common cause of perioral dermatitis is a topical steroid. Typically it seems to get better, but rebounds worse. Usual treatment is withdrawal of steroid, tolerating withdrawal exacerbation, use of non-steroid antiinflammatory such as tacrolimus, oral doxycycline or minocycline at 50 or 100mg a day. Treatment will require several months.