There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Therapeutic Benefits of Skin Toner
- Skin toner has been shown to have therapeutic benefits when used as part of a comprehensive skin care routine 1.
- A study found that an advanced skin care routine that included a toner outperformed a simple routine in improving superficial hydration, deep hydration, skin roughness, and reducing melanin heterogeneity and crow's feet wrinkle depth 1.
- Another study found that a guava toner significantly reduced oiliness on the forehead and nose, making it a potential treatment for oily skin 2.
- Skin toner has also been shown to improve skin hydration when used in combination with other moisturizers, such as cream and spray water 3.
Comparison with Other Skin Care Products
- A study compared the moisturizing effects of cream, toner, and spray water, and found that the combination of cream and toner led to the greatest hydration change rate for normal skin 3.
- Another study found that green tea extract, which is often used in skin toners, has antioxidant and moisturizing effects on the skin 4.
- Vitamins, such as vitamins C and E, which are often included in skin toners, have also been shown to have therapeutic benefits for the skin, including protecting against environmental insults and improving skin conditions such as acne and psoriasis 5.
Specific Benefits of Skin Toner
- Skin toner has been shown to reduce hemoglobin heterogeneity, improve skin brightness, and reduce nasolabial wrinkles 1.
- Guava toner has been shown to have anti-sebum efficacy, making it a potential treatment for oily skin 2.
- Skin toner has also been shown to improve skin hydration, reduce skin roughness, and improve skin microrelief 3, 4.