الحناء
A plant dye applied to hair and skin, mentioned in reports about grooming practice and discussed by commentators for minor topical complaints.
مَا مِنْ دَاءٍ إِلَّا وَالْحِنَّاءُ لَهُ دَوَاءٌ
“There is scarcely an ailment for which henna does not offer some remedy.” (meaning, not a literal translation)
Henna's use as a hair dye is better attested through general practice reports about companions dyeing grey hair than through this specific broad medical claim, which is worth reading as commentary-tradition color rather than an authenticated Prophetic guarantee.
Ibn al-Qayyim and al-Dhahabi both describe henna's cooling, astringent quality — traditionally applied to minor burns, cracked skin, and as a hair conditioner and dye. They note its use narrowing over time from the broad ailment-list this weak saying suggests toward its more consistently attested uses: dyeing hair and treating minor skin irritation.
Modern cosmetic and dermatological use of natural henna is well established for hair dyeing and temporary skin art, with genuine mild astringent properties recognized; the broad ailment-curing claim in the hadith above isn't something modern research addresses or supports at that scope.