When I drink Starbuck's cafe mocha I get significant irritation on my face. It affects the skin between my eyes, my cheeks, the crevices of my nose and my chin. At times it has spread to my scalp. It can also affect the center of my chest. It mainly just looks bad but the affected skin can be tender and sting. Without further exposure the redness lasts a few days.  After researching the ingredients it seems likely the potassium sorbate ingredient is the cause, though it will take exposure to potassium sorbate through other products to be certain. 

Starbuck's cafe mocha is made with Fontana Bittersweet Chocolate Mocha Sauce which contains this ingredient. The ingredients for the Fontana sauce can be seen here:  http://www.starbucksfs.com/Products/Details/Bittersweet_Chocolate_Sauce - Rick, by email

Sue's comment:

I agree that potassium sorbate (preservative E202) seems the most likely cause of facial irritation.  It is well documented in the medical literature that sorbic acid and potassium sorbate can cause contact dermatitis but less well known that foods containing sorbates can cause erythema (reddening of the skin), most frequently on the face and back, worse in people with rosacea.

Reference: CRC Handbook of Food, Drug and Cosmetic Excipients, page 366 

See 200-203 Sorbates factsheet

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