Like a perfect date or the secret ingredient in grandma's pie, sensitive skin is hard to define.
Often, it's a subjective sensation that we self-report, because we know our bodies better than any clinical test. Some people are more prone to it if they suffer from a condition like rosacea or dermatitis.
Since we rely so much on self-diagnosis, rather than something objectively measurable, it’s difficult for skincare product formulators to meet our needs. Sensitive skin is now accepted as a major dermatological problem with physiological origins — and we're still totally mystified by it.
More than 50% of the Western population has issues with sensitive skin (Farage and Maibach, 2010).