Intro: For Jews living outside of Eretz Yisrael, Yom Tov means two days each. (Only Rosh Hashanah is two days everywhere.) The origins of the two-day Yom Tov is the subject of a major Talmudic and halachic discussion, of which our forum is not suited. Of interest to our study of halacha is whether there are any distinctions between the first day and the second day. Generally, no! In fact, the Sages exhort us to treat Yom Tov Sheini (the second day) with the same sanctity and respect as Yom Tov Rishon (first day). Our siman discusses the slight differences between them. One difference relates to the treatment of the dead. For the other, we will excerpt from Rav S.B. Cohen’s The Laws of Yom Tov, p. 236-237, for a practical and brief summary:
“The Second Day of Yom Tov. The second day of Yom Tov (with the exception of the second day of Rosh Hashanah) is treated more leniently than the first day with regard to the laws of treating illness. The Sages permitted anyone suffering from even a minor ailment to perform a Rabbinic prohibition in order to alleviate his discomfort. With regard to Biblical prohibitions, however, there is no special leniency on the second day of Yom Tov. Thus, it is permitted to take Tylenol (Ed. or other medication) for a minor headache on the second day of Yom Tov. Likewise, it is permitted to carry medicine for a minor ailment through a ‘karmelis’, where carrying is prohibited only Rabbinically. (Ed. You may be wondering – isn’t carrying always permitted on Yom Tov? Yes, but only where there is a legitimate Yom Tov need. Were it not permissible to take the medicine, carrying it would not be permitted either, even through a Rabbinically-prohibited area!) Another example pertains to the treatment of irritated skin. This condition is not serious enough to warrant medication on Shabbos or on the first day of Yom Tov, but it may be treated with ointment on the second day. As explained in Chapter 26, dense creams are subject to the melacha of ‘memaraiach’ (smoothing), under Biblical law, whereas creams with a loose consistency are subject to this melacha Rabbinically. (See p. 200-201 for the definitions of “dense” and “loose”.) Thus, on the second day of Yom Tov, one may apply ointment that has a loose consistency to irritated skin. See below for a detailed discussion of diaper rash.”
[Ed. If you would like more on the subject of medical treatment or the treatment of minor ailments on Shabbos or Yom Tov, please ask me, and I will send you something from the “MBY Archives” (drool…!)]
Ed. This siman is also the address for the halacha of a resident of Eretz Yisrael who spends Yom Tov in the Diaspora and a resident of the Diaspora who spends Yom Tov in Eretz Yisrael.
I will mention just two basic points on these issues:
1) The resident of Eretz Yisrael who visits the Diaspora is forbidden to act in a way that will demonstrate publicly that he is not observing the second day of Yom Tov. This halacha is not sourced in the laws of Yom Tov per se, but in a general requirement to act in accordance with local practice.
2) A resident of the Diaspora who is temporarily visiting Eretz Yisrael is still required to observe Yom Tov Sheini. Based upon the aforementioned principle of acting in accordance with local practice, he should be discreet in his Yom Tov observance while in the presence of those for whom it is Chol Hamoed or a regular day. Notably, however, there is less deviation from local practice when someone observes Yom Tov while everyone else does not than when someone does not observe Yom Tov while everyone else does! See why?
Each of these last two points is subject to considerable discussion and qualification and should be addressed to a Rav for particular application.