Ki Seitzei, Devarim 25:1, Lo Yilbash and Men's Hair Dye. לא ילבש גבר שמלת אשה

The Mechaber (YD 182:6) says that it is assur for a man to dye his hair.

אסור לאיש ללקט אפילו שער אחד לבן מתוך השחורות, משום "לא ילבש גבר", וכן אסור לאיש לצבוע (שערות לבנות שיהיו) (ב"י) שחורות, אפילו שערה אחת

However, if a man is afraid that his white hair makes him look old and it will jeopardize his job, Reb Moshe (YD I:82 and YD II:61) and Reb Moshe Mordechai Epstein (Teshuvos 24) say that it is muttar for him to dye his hair.  He is not motivated by an effeminate desire to be beautiful, he just wants to keep his job and earn a living.  This can also be found in the Sefer Chasidim (siman 379,) where a man was advised by his friends to dye his hair to improve his shidduch prospects.  It is apparent that Reb Yehuda HaChasid's only concern was the duplicity, not the halacha of Lo Yilbash.

אמרו לאחד: אישה פלונית יפה במקום פלוני, היא חפצה בך. שמע לעצתנו, ולך שמה ותצבע שעריך בשחור, ותהיה סבורה שאינך זקן, והיא תאמר מה שבלבה. אמר להם: חלילה לי להטעות אותה אלא תראה שאני זקן

Similarly, see Tosfos Nazir 59a DH Mabul and Tshuvos HaRashba brought in Beis Yosef 182 that כל שאינו עושה משום נוי שרי.  I assume that a toupe is subject to the same analysis, and I know one yarei shamayim, who wears a toupe for business reasons.  He does not wear it when he's not in a work environment.  Because this man asks Rav Shmuel Kaminetsky before doing anything questionable, I assume he does this pursuant to a psak halacha.

The question is, what would the halacha be today, when many men dye their hair for appearance' sake. Would the issur no longer apply?  Would it be muttar to dye your hair just for appearance' sake? (See article in the Los Angeles Times that discusses the two motivations we mentioned and cites statistics on the growing trend of men dying their hair.)  It appears obvious that the halacha would change as social behaviors change.  Almost everyone relies on this when they look at the mirror or wear deodorant or cologne, leaving aside the question of whether this reliance is applied too broadly.  We know that in biblical times, many men wore earrings.  Now, it probably would be assur for a man to wear earrings.  Does this apply to dying hair?

On the one hand, the teshuvos we cited are not proof of hetter, because they were addressing cases where the person was motivated only by a need to achieve a specific goal of parnassah or shidduch, while we are talking about a behavior motivated by what the Gemara considers a feminine obsession with appearance and a desire to disguise one's age and maintain an illusion of youth.  On the other hand, it is no longer something associated only with women.  

This might be a machlokes between the Mechaber and the Rema in YD 182:6.  

In some places, men would absolutely not shave the hair under their arms.  In other places, men would commonly do so.  The Mechaber says, quoting the Rambam (12 AZ 9), 

המעביר שער בית השחי ובית הערוה אפילו במספרים כעין תער היו מכין אותו מכת מרדות בד"א במקום שאין מעבירין אותו אלא נשים כדי שלא יתקן עצמו תיקון נשים אבל במקום שמעבירין אותו גם האנשים אם העביר אין מכין אותו

The Gaon there (182:1-3) says that according to this shittah, even in a place where both men and women shave their bodies, it is assur for a Jewish man to do so, but only lechatchila, and so there would be no malkos.

On the other hand, the Rema says

ואפילו לכתחילה שרי (ר"ן פ"ב דעבודת כוכבים) רק החברים נמנעים בכ"מ (שם ובב"י בשם נ"י

that it is muttar lechatchila, and that only Bnei Torah refrain from doing so.
The Rambam's issur lechatchila, it seems, stems from the fact that Chazal decided that such behavior is not al pi din gender specific, and is not really assur, but it is still a feminine type of behavior and should be avoided by Bnei Torah. 

This machlokes might apply, or might eventually apply, to the question of men dying their hair.

It is possible, however, that the comparison to the issue of shaving the body is imperfect.  In that case, the motivation for men to do it is the discomfort of sweat accumulating on the hair, not to be pretty.  If the men in that area did it for beauty's sake, it is possible that everyone would prohibit it.  However, I have not found any poskim that focus on this distinction, so I am not willing to propound it as a matter of practical halacha.

• Assuming that we would pasken like the Rama, a number of questions remain.  If the numbers cited include homosexual men, the statistics would be meaningless, because it is davka those men the Torah warns us not to be like, so their habits could not possibly be the basis of a hetter.  On the contrary- the fact that they do this would be the basis of additional issur.  
• If the numbers include men that in Orthodox Jewish society would be viewed as effeminate, would that render the numbers irrelevant?  Perhaps not.  Not too long ago, only low women dyed their hair or wore very high heels or red clothing.  Behaviors mostly specific to prostitutes slowly percolated "upwards," and now are not seen as pritzus at all.  In other words, irrespective of the origin of the behavior, once it becomes common it loses its previous connotation.
• Assuming the numbers are legitimate and have halachic validity, at what point does it become "not a feminine practice?"  One could argue that this would be true even at a low number, so long as it is not immediately viewed as feminine.  On the other hand, one might say that for the halacha to change would require a higher percentage.  
• Another question is, and assuming that prevalence is determinative, would we judge each city separately?  Each country?

The Prisha in 182 touches on this, but does not resolve the question.

 אבל במקום שמעבירין השער האנשים. נראה דרצונו לומר אנשים נכרים לטון דנהוג נהוג ולמדינן ממנהג הנכרים גס יש לומר דעל ישראל קאמר דהיכי דהנהיגו כן כולם יחד אין מוחין בידם

Reb Akiva Eiger brings down this Prisha and also brings a Teshuva of the Perach Shoshan,   פרח שושן כלל ו׳ ס״ב which can be found here, with the relevant paragraph being the last one in the teshuva on the next page.  As far as I can tell, the Perach Shoshan just brings down the Prisha, so it seems that Reb Akiva Eiger brings it only to show that the question remains unresolved.

Rabbi Tzvi Hersh Haber of LA posted on this topic here.  In his comments on our post he quotes a local rabbi to the effect that "Rav Elyashiv told him with regards to tzniyus, things that are tzibbur dependent are dependent on the tzibbur that is מקפיד בדברים אלו."

Here's a cartoon from the New Yorker that encapsulates the problem I am dealing with.  It is available for purchase in Premium Giclee Print from Conde Naste for $139.

All things considered, there is adequate justification for the men that are meikil. Even if it were problematic, מוטב שיהיו שוגגין ואל יהיו מזידין would very likely apply.  Certainly, this is less of a problem than those men that shave all the hair off of their heads as smooth as a cue ball, as we discussed elsewhere.

☞UPDATE:
Thank you LkwdGuy for sending a mareh makom to Rav Mordechai Tendler's Mesores Moshe, pg. 248, quoting Reb Moshe that if it is common for men to dye their hair then there is no issur lo yilbash, similar to looking in a mirror.
As I respond in the comments, we cannot pasken from the Mesores Moshe as easily as we can from the Igros.  Reb Moshe was extremely meticulous when he wrote a teshuva he intended to be mefarseim, weighing every word, while oral discussions, and even oral psakim, might have been oriented toward the individual with whom he was talking, or intended to make a point in the interpretation of a sugya, and not intended as a psak for the generations.  Still, it does show that Reb Moshe held that the svara is valid.  The problem remains that in our time, as I illustrated with the cartoon, the increasing frequency of men dying their hair might not be determinative.  A large part of that group might be men whose gender identity is not masculine, and so they might not count.