In the books of Imams Al-Bukhari and Muslim 
it is narrated that Anas 
said: "The Messenger of Allah 
has allowed Abdur-Rahman Ibn 'Awf and Az-Zubayr Ibn Al-'Awwam 
to wear silk garments because of a skin rash they had." In another narration, "Abdur-Rahman Ibn 'Awf and Az-Zubayr Ibn Al-'Awwam complained to the Prophet during a battle that they had a skin rash, and he allowed them to wear silk garments which I saw them wearing."
There are two areas of interest regarding this narration, one in the area of Fiqh (Islamic Jurisprudence) and another medical.
In the area of Fiqh, in principle, wearing silken garments is allowed only for women and is disallowed for men, except when there is a legitimate need. For instance, men are allowed to wear silken garments in cold weather, when one has only a silken garment to wear and when complaining from mange, rashes, mites or lice, as evident by the last narration.
According to Imams Ahmad and Shafi'i wearing silken garments is allowed for men if a necessity warrants it. The permission given to some Muslims due to special circumstances applies to all those who face similar circumstances.
Several scholars said that the narrations that prohibit silken garments for men apply in general. They said that the aforementioned narration might entail a specific permission for only 'Abdur-Rahman Ibn 'Awf and Az-Zubayr . They say that it is possible, though, that this permission applies to other Muslims. When there is a probability regarding a certain ruling, adhering to the general text is warranted. This is why some of the narrators of this narration commented: "I do not know if the permission does apply to whoever comes after them ('Abdur-Rahman Ibn 'Awf and Az-Zubayr)."
The correct opinion is that the permission is general in its indication and that there is no evidence that it is specific or restricted. Similarly, the Prophet once said to Abu Burdah: "This permission applies to you and none else after you." Also, Allah said to His Prophet, sallallaahu alayhi wa sail am, regarding the woman who offered herself in marriage to the Prophet (what means):
"...A privilege for you only, not for the (rest of the) believers..." [Quran, 33:50]
In the medical area, silk is produced by an animal and is a remedy. Silk has many benefits, such as soothing and strengthening the heart and helping relieve several of its ailments. Silk also helps against black bile and whatever ailments it might cause. Further, silk strengthens the eyesight when used as eyeliner. Raw silk, which is used in preparing medications and remedies, is hot and dry in the first degree. When silk is used in clothes, it is mild and heats the body. Sometimes it could chill the body.
Ar-Razi 
said: "Silk is hotter than linen, colder than cotton and develops the flesh. Every type of thick clothes weakens the body and hardens the skin."
There are three types of clothes, one that brings warmth and also heats the body. Another type f clothes brings warmth but provides no heat to the body. The third type does not bring warmth or heat. There is no type that brings heat but not warmth to those wearing it. For instance clothes made of wool and animal hair elevate body temperature and bring warmth to the skin. On the other hand, silk, Kittan (linen) and cotton garments only bring warmth to the skin. Kitten clothes are cold and dry, wool clothes are hot and dry, while cotton garments are moderate. Silken garments are softer and less hot than wool. The author of Al-Minhaj stated that wearing silk, "Does not bring as much warmth as cotton, because it is milder."
Every type of soft, polished clothes heat the body less and in less effective in helping the decomposition process. That is why it is better that this type of clothes is worn during summer and in hot areas.
Since silken garments are neither dry nor thick as the other types of clothes they help as a treatment for skin rashes that result form dry, thick material. Hence, the Prophet allowed Az-Zubayr and 'Abdur-Rahman to wear silken garments due to their skin rash. Also, silken garments are the least hospitable to mites or lice, for it is not the best environment where mites live and thrive.
The types of body wear that neither elevates the body temperature nor brings warmth are made of iron, lead, wood, sand, and so forth.
If one asks, "since silk provides the best type of clothes and the most suitable for the body, why was it prohibited for men by the Islamic legislation, which is the mot honorable, perfect legislation and which allows the good and pure things and only prohibits the impure things?
Scholars answered this stating different reasons, such as, that Islam prohibited silken garments for men so that they observe patience and abandon wearing them for Allah's sake. Others say that silk was prohibited because it leads to arrogance and pride.
Yet others say that silk was prohibited because of its softness on the skin that leads to feminine behavior while weakening manhood and masculinity. Hence, you rarely see a man wearing silken garments who is not affected by its softness by inadvertently imitating feminine behavior and softness, even if he was among the most masculine men. Wearing silken garments will certainly diminish the manly qualities and masculinity, although these qualities will not disappear all together.
As for those who do not comprehend these facts, let them submit to Allah's wise decisions and adhere to the texts that prohibit it for men.
The Prophet said: "Allah has allowed silk and gold for the females of my nation and prohibited them for the males of my nation.” [An-Nasa’i]
In another narration, the Prophet said: "Wearing silk and gold is prohibited for the males of my Nation and allowed for the females."
