Fasting insulin is a blood measurement of how hard your pancreas is working to keep your blood sugar normal after an overnight fast. It's often the earliest measurable signal of metabolic strain — shifting years before HbA1c or fasting glucose do.
For skin, elevated insulin is particularly consequential. Insulin drives IGF-1 signaling, which stimulates androgen activity and sebum production. Kraft's clinical work established that fasting insulin patterns identify metabolic dysfunction long before glucose reveals it (Kraft, 1975; contemporary reviews in DiNicolantonio, 2017).
The skin patterns associated with elevated insulin: adult acne (particularly along the jawline and chin), oily skin, larger visible pores, and skin tags. These are especially common in women with PCOS, where insulin resistance and androgen excess reinforce each other (Diamanti-Kandarakis, 2012).
Clinically, fasting insulin below 10 μIU/mL is generally considered normal, but the range associated with metabolic optimization for skin (and long-term health) is 2-6 μIU/mL. Anything above 8 in a woman with symptoms of adult acne or metabolic changes deserves attention.
Interventions with strong evidence: resistance training (Colberg, 2016), reducing refined carbohydrates, eating protein and fiber before carbs, adequate sleep, and stress management. Insulin often moves quickly with these interventions — within weeks.
Fasting insulin is one of the nine biomarkers on the JenSkin panel because it's often the earliest and most actionable signal in a woman's panel.