According to Phyto, our hair starts to become weaker and more fragile after the age of 30. Phytodensium Serum is supposed to address this with ingredients that protect against the environment and free radicals. It has extract of horsetail, a plant that Europeans have long used to heal wounds, strengthen hair and as a diuretic. I don't know if there is any hard evidence that it is really beneficial for the hair. There is also walnut and sunflower, plus blackcurrant and vitamin B6. Interestingly, there is also a derivative of tyrosine, an amino acid that is a precursor of melanin that may help to inhibit the appearance of gray hairs.
Phytodensium Serum is a leave in potion and I've just started to try it. It passes the first test of not irritating (despite the metabisulfate and phenoxyphenol) and my hair looks soft and shiny. Time will tell whether it has any real effect on hair strength and keeping out those grays.