(photo credit: MCT)
Treating hair infested with lice is never fun, yet parents remain responsible to
promptly and thoroughly clean their children (even if this includes school
absence!) and homes to prevent it from infesting others.
more complex on Shabbat, when it is biblically prohibited to kill any creature
unless it poses an acute health danger.
Lice, however, might be an
exception to the rule, and actually present us with a fascinating case of the
tension between Jewish law and contemporary science.
After recording the
general prohibition of killing creatures, the Sages (Shabbat 107b) asserted that
one may kill lice since they “do not reproduce” but instead generate
spontaneously from sweat (MB 316:38). The Sages adopted the widespread ancient
belief, articulated by Aristotle and others, in “spontaneous generation,” which
claimed that some life does not emerge from seeds, eggs or parents. Belief in
spontaneous generation remained widespread until Louis Pasteur entirely debunked
the theory in 1859, although skeptics had questioned aspects of the theory for
two centuries beforehand.
The Sages asserted that the prohibition of
killing on Shabbat only applied to sexually reproduced creatures. They similarly
exempted asexually reproduced organisms from the biblical prohibition of
consuming insects (Leviticus 11:10-11), and subsequently permitted consuming
worms found within the flesh of fish or fruit (YD 84:16).
With regard to
non-legal matters, many scholars, like Maimonides’s son, Rabbi Avraham (d.
1237), have stated that despite our reverence for the talmudic sages, their
statements regarding medicine, natural science and astronomy remain entirely
non-authoritative (Ma’amar al Aggadot Hazal). Matters become more complex,
however, when faulty scientific assumptions were the basis for legal
No consensus has emerged regarding the status of these
laws, with acrimonious debate occasionally dividing the scholarly
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This controversy recently exploded over the widespread discovery
of the Anisakis worm in the flesh of many popular kosher fish, including wild
salmon, flounder, sardines and herring.
These worms are parasites whose
eggs regularly travel through the aquatic food chain until they ultimately
emerge in the organs and flesh of a large host fish.
Since the worms also
appear in the cavity of the fish, and their origins are well-documented,
contemporary decisors like Rabbis Yosef Elyashiv and Shmuel Wosner (Shevet
YD 4:83) have asserted that one must assume these worms are not identical
to the permissible creatures mentioned in the Talmud.
As such, their
followers have produced lists of regularly contaminated fish to carefully
inspect or avoid. This approach, in practice, accepts contemporary scientific
analysis, while avoiding any claim that the Sages held errant scientific
beliefs. Elyashiv has reportedly adopted a similar approach with lice, thereby
prohibiting killing them on Shabbat (Teshuvot Shevet Hakehati
Others, including Rabbi Yisrael Belsky of OU Kosher, have
defended the continued consumption of these fish by citing numerous historical
sources (Teshuvot Imrei Yosher
2:11) which indicate that decisors have been
aware of such worms, yet continued to maintain the talmudic rule that insects
found within the flesh do not affect the kashrut status of the fish (Shulhan
84:51). Nothing has changed, asserts Belsky, and there is no reason to
depart from the historical practice.
Of course, this approach does not
address the fact that the entire dispensation for worms in fish flesh was based
on a now-debunked scientific theory. Historically a few rabbinic figures denied
contemporary science because they believed that was necessary to defend this
talmudic law. This approach was criticized by Rabbi Yitzhak Lampronti (Italy, d.
1756), who asserted that the Sages were limited by the knowledge of their times.
If Jewish law does not reform from its incorrect scientific assumptions, then
people might violate Shabbat by killing lice (Pahad Yitzhak,
While Rabbi Yosef Kapach adopted this approach, Rabbi Eliyahu
Dessler countered that the unalterable talmudic law was based on ancient
traditions and not solely on scientific assumptions. He and Rabbi J. David
38:4) have further suggested that the Sages based their
assessment on the fact that the sexual reproduction of lice is unperceivable to
the eye, and that contemporary findings do not alter that legal
Rabbi Natan Slifkin (Sacred Monsters
) has recently advocated a
different approach found in the writings of Rabbis Moshe Glasner (Dor Revi’i,
) and Isaac Herzog (Heichal Yitzhak
OC 29). These figures acknowledged
that contemporary science was correct and that the Sages errantly believed in
spontaneous generation, but asserted that talmudic law had become canonized and
should not be altered. Thus the dispensation to kill lice remains authoritative,
even as we acknowledge that the initial scientific assumption behind the law is
no longer true.
Even if one adopts a lenient position regarding killing
lice, other prohibitions, such as pulling out hair or squeezing water from it,
might preclude intensive treatment of lice infestation on Shabbat, and one
should consult with their rabbi for further guidance.The writer, online
editor of Tradition and its blog Text & Texture (text.rcarabbis.org),
teaches at Yeshivat Hakotel.JPostRabbi@yahoo.com
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