- Nourishing Scalp & Hair Serum. Formulated with a unique blend of Evening Primrose oil, SP94, and Powerdose Light, the deeply nourishing Sérum de Force scalp serum helps fortify hair from the roots at the onset of growth. Apply directly to scalp and massage serum into roots. Luxuriously nourished, deeply hydrated and replenished hair through essential oils. Evening Primrose Oil: Derived from the seeds of the primrose wildflower, it offers an essential fatty acid, gamma-linolenic acid (GLA).