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 Astringent Toner
- Astringent toner has been shown to have therapeutic benefits, particularly in reducing oiliness and improving skin hydration 1, 2.
- A study on guava toner found that it significantly reduced oiliness on the forehead and nose, making it a suitable daily application for improving skin efficacy 1.
- Another study compared the moisturization effects of cream, toner, and spray water, and found that toner applied with repeated toner every 2 hours was efficacious for skin hydration, especially for normal skin 2.
Natural Ingredients and Skin Benefits
- Natural ingredients, such as those found in herbal medicines, have been shown to have therapeutic benefits for atopic dermatitis, including inhibition of cytokine and chemokine expression, IgE production, and inflammatory cell infiltration 3.
- Green tea extract has been found to have moisturizing effects and improve skin microrelief, making it a beneficial ingredient in cosmetic formulations 4.
Skin Tone Correcting and Hyperpigmentation
- A non-hydroquinone, multi-action skin tone correcting cream has been shown to be effective in reducing dyschromia and melanin index, and improving overall skin appearance 5.
- The use of astringent toner in combination with other skincare products, such as moisturizers and creams, may enhance its therapeutic benefits and improve skin hydration and tone.