All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If what you meant is that a man applies henna to his hands and feet, then it is not permissible to do so, neither in marriage nor outside marriage unless for the purpose of treatment. That is because it is a beautification peculiar to women and it is not permissible to imitate women in dress (clothing) and beautification.
The evidence that henna is peculiar to women, is that ‘Aa’ishah said: “A woman made a sign from behind a curtain to indicate that she had a letter for the Prophet so the Prophet closed his hand and said: ''I do not know whether it is a hand of a man or a woman? She replied: “Rather, it is a hand of a woman.” He () said: “If you were a woman, you would have changed your nails (meaning dyeing them with henna).” [Abu Daawood, An-Nasaa’i and Al-Albaani graded it as Hasan (good)]
The second evidence is that Abu Hurayrah narrated that a hermaphrodite who had dyed his hands and feet with henna was brought to the Prophet so He asked: “What is the matter with him?” They (the Companions) replied: “O Prophet of Allaah, he imitates women. So, the Prophet ordered regarding him to be banished to An-Naqee’ah. (a name of a place). They (the Companions) asked: “Should we not kill him?” He [the Prophet] said: ''I have been forbidden from killing the people who perform the prayer.” [Abu Daawood, and Al-Albaani classified its chain of narration as Saheeh [sound]
An-Nawawi said: “It is desirable for a married woman to dye her hands and feet for the well-known Ahaadeeth (in this regard), but this is forbidden for men except when in need of treatment.”
Also, among the evidence that it is forbidden, is that the Prophet said: “Allaah has cursed men who imitate women and has cursed women who imitate men." [Al-Bukhari]
On the other hand, if what you mean is dyeing the grey hair with henna, then the view we believe to be the most preponderant is that this is permissible as Abu Tharr narrated that the Prophet said: “The best things to use to change grey hair are henna and katam (a kind of dark henna)." [Ahmad and Ibn Maajah] For more benefit, please refer to Fatwa 91006.
Besides, it is permissible to use henna for the purpose of treatment and Ibn Al-Qayyim mentioned many of its benefits in his book “The Prophetic Medicine” where he stated that it is used in treating headaches and other ailments. He also mentioned a number of Ahaadeeth about the permissibility of treating with henna but their chains of narrators are Dha’eef [weak].
Allaah Knows best.