Rosemary essential oil, which is distilled from the flowers and leaves, contains a number of chemicals that contribute to the effects of the herb. Rosemary oil tones and firms the skin. The herb is an astringent, helping to reduce excess oil in skin and hair, according to Frontier Natural Products. Rosemary tones and firms sagging skin, and it is used as an ingredient in anti-aging products. The disinfectant and antibiotic properties of rosemary contribute to its use for treating acne, dermatitis and eczema, according to Guide to Herbal Remedies. Rosemary Also increases blood flow and contributes to healthier skin. The circulatory benefits of rosemary lead to an improved complexion, allowing nutrients to effectively reach the skin while removing waste products and toxins. Rosemary oil improves skin tone by reducing puffiness and swelling.