We Orthodox Jews tend to get the heebee jeebies when it comes to nails (the ones that grow on fingers and toes, not the ones that are intentionally hit with a hammer).

What is the background of this? A brief history:

The Gemara (Moed Katan 18a, Niddah 17a) says that there are three types of nail cutters – righteous, pious and evil. The righteous bury their nails, the pious burn them and the evil people just throw them down.  The Gemara goes on to explain that the problem with the nails being in a public place is that a pregnant woman may step on them.

So what’s the big deal if a pregnant woman steps on nails? The Ran offers two explanations; her revulsion upon seeing them may cause her to miscarry, and “keshafim”, or evil spirits, are associated with nails. (We’ll get back to that).

The Pri Megadim (OC 260) offers the following:

Adam HaRishon was created covered by nail like material over his skin. After the sin it was removed, remaining only on his fingers and toes. Since Woman is generally blamed for the original sin, there is therefore a danger for pregnant women to step on finger and toe nails.

The Gemara (Ibid) qualifies this law by saying that if the nails are moved there is no danger. Therefore in a Beis Medrash or other place where women are not common one doesn’t have to worry, even if they will be swept up and placed outside. The Elya Raba writes that perhaps they have to be moved to an entirely different room.

Based on the above it would be prudent for a pregnant woman to avoid a nail salon.

Rav Steinman writes that he asked the Chazon Ish how come we don’t see women miscarrying due to a lack of diligence and knowledge of these laws? The Chazon Ish replied that as we are living in a time of Hester Panim there is ‘static’ between us and the spiritual powers associated with these dangers and there is therefore less of a risk.

Some other rules of (thumb)nails:

• Not to cut on Thursday because they will sprout (presumably this means noticeably) on Shabbos.
• Not to cut finger and toe nails on the same day (Mogen Avrohom 260). (Shulchon Hatahor recommends averting this problem by leaving one toenail uncut).
• Only cut fingernails Erev Shabbos and Yom Tov (Ibid).
• Based on the above the Mogen Avrohom recommends cutting toenails on Thursday and fingernails on Friday.
• Not to cut nails on Rosh Chodesh (R’ Yehuda Hachassid quoted in Ba’er Haitiv OC 260).
• The Rema says not to cut fingernails in order. The order he gives is 42531 for the left hand and 24135 for the right. The Arizal laughed at this practice and the Maharam Miruttenberg was not particular about this. The Mogen Avrohom recommends being stringent. There are various opinions as to which hand to cut first, the Rema seems to favor the left. (See Pri Megadim and Ashel Avrohom Mibutshetsh).All this does not apply to toenails. (Chazon Ish).

The Aruch Hashulchan (OC 260:6) writes that all of the above are not halachic obligations rather one who is careful should be, and one who is not doesn’t have to start.

Shabbos

There is a definite preference for one to cut their fingernails on Friday in honor of Shabbos. It is a matter of dispute as to when is the correct time to do this, some say specifically in the morning, others choose the afternoon. Some say before the Mikvah, others say after.

Netilas Yadayim and Tevilah

Dirt on hands is considered a chatzitzah, or separation, for ritual hand washing and would have to be removed before washing for bread. The same applies for dirt under nails, but only on the portion of the nail that extends beyond the finger. For immersion in a Mikvah we are more stringent and require that the nail be completely clean, therefore we cut them for tevilah.

Klipos

As mentioned, there are evil spirits associated with nails. Although I have absolutely no understanding of this, it seems that the part of the nail that extends beyond the finger contains little bad guys and the part that is near the skin contains the really good guys.

Havdalah

The Rema (OC 298:3) quotes the Zohar that when one makes the blessing on the candles during Havdalah on Motzai Shabbos one should look at the nails of their right hand with the hand curled inward and the thumb tucked away out of sight.

The Mishna Berura explains that one has to have enough benefit from the light to differentiate between different coins. We ascertain this by differentiating between the nail and the finger which are of similar color. He adds that nails are considered a sign of blessing because they are constantly growing. I’m not sure why we avoid the thumb, if anyone knows please let me know.

Chol Hamoed

It is forbidden to cut nails on Chol Hamoed under ordinary circumstances unless they were cut on Erev Yom Tov or for a mitzvah (e.g. Mikvah).