Flaky/Itchy Scalp Toner

The base most products are built on. It carries the other ingredients and has no safety concern.

A fast-evaporating solvent used to carry actives and give toners a light, "clean" feel; at the concentrations used in classic astringents it can be genuinely drying or irritating with repeated use, especially on dry or compromised skin, though it is not inherently toxic and is a normal, well-studied cosmetic ingredient.

A quaternary ammonium antimicrobial used as a preservative and, in scalp products, to keep flaking microbes down. It is an established irritant for some people at higher concentrations, and eye contact should be avoided; at the low levels allowed in cosmetics most people tolerate it without trouble.

A cooling counterirritant used in scalp tonics, lip balms, and muscle rubs. The tingle is the ingredient working on nerve endings, not a sign of damage, but higher levels can genuinely irritate, and sensitive or broken skin is better off without it.

An anti-dandruff and anti-fungal active common in European scalp products, often as the gentler alternative to zinc pyrithione. The EU scientific committee (SCCS) has reviewed it and it is well tolerated at use levels in rinse-off and leave-on scalp products.