April 8, 2024
Close this search box.
Close this search box.
April 8, 2024
Close this search box.

Linking Northern and Central NJ, Bronx, Manhattan, Westchester and CT

Responses to Critiques of Our Permitting All Electric Shavers

By Rabbi Haim Jachter

Part II

Reactions abound to the “Halachic Haircutting Handbook” we released in June 2021, especially to our strong support of Rav Hershel Schachter and Rav Mordechai Willig’s baseline permission of all electric shavers. We document that the Chochmat Adam, Chafetz Chaim, Kitzur Shulchan Aruch, Aruch Hashulchan and Rav Moshe Feinstein all permit a misparayim ke’ein ta’ar (scissors like a razor) that leaves a clean shave (although the Chatam Sofer and Chazon Ish disagree). Therefore, electric shavers are halachically permissible according to the consensus of poskim. We argue that all electric shavers function as a misparayim ke’ein ta’ar, making testing individual models and shavers unnecessary for halachic permissibility. According to the Chochmat Adam, Chafetz Chaim, Kitzur Shulchan Aruch, Aruch Hashulchan and Rav Moshe Feinstein, all electric shavers are permissible. According to the Chatam Sofer and the Chazon Ish, all are forbidden (unless special modifications are made to the shaver to ensure it does not leave a clean shave).

Last week, we responded to five critiques of our assertions; this week, we conclude by presenting our answers to five points raised by critics:


Critique No. 6

The March 2015 issue of the “Journal of the Mechanical Behavior of Biomedical Materials” includes an article stating that a blade in a rotary shaver can cut without the screen’s counterforce. The paper sets forth the values for the blade’s thickness and angle. It also addresses the question of blade speed (see 4.7).


Response to Critique No. 6

On the contrary, a careful examination of the article proves our contention. The report states, (4.5) “for typical dry shaving conditions, hair is cut simultaneously by the blade and foil edge. They are like a pair of scissors.” However, the article says (5) blades with a small wedge angle cut the hair without contact with the foil. However, top experts told us that in practice, electric shavers employ larger angles—65 to 75 degrees. Shaving machines are designed to last long; therefore, a larger angle is used to ensure the shaver works as scissors. By contrast, razors are positioned at a sharp angle and are very sharp—that is how they cut against the skin. However, they last a very short amount of time.

The PowerPoint from Philips Norelco clarifies that at the large angle in which the blades of the electric shaver are positioned, they cannot function as a razor but only as scissors, exactly what the “Journal of the Mechanical Behavior of Biomedical Materials” article states.

Now, we can explain the difference between a razor, for which facial skin provides a sufficient counterforce to cut hair and an electric shaver which it does not. The article provides the answer—the angle makes a great difference. Razors cut at a sharp angle and act as a forbidden ta’ar. The small amount of counterforce supplied by the skin suffices for a sharp razor cutting at a very acute angle. Electric shavers are positioned at a large angle and function as permitted scissors. The skin provided insufficient counterforce for blades’ cutting at such large angles as in electric shavers.

Blade geometry makes a significant difference. For durability, shaver manufacturers are willing to share the stress between the screen and the blade rather than have a single sharper blade.

The article archived at: https://www.sharpeningsupplies.com/Detailed-Discussion-on-Knife-Sharpening-Angles-W28.aspx arrives at the same conclusion: the smaller the blade’s angle, the less force is required to cut with it. It also notes that a slimmer angle is much more prone to damage. This article even provides ranges of angles and how durable versus easy to cut with each range. “Any edged tool or knife that is sharpened past 30 degrees will be very durable. Its cutting ability will be noticeably reduced. This durability has an advantage because more force can be used to make the cut. While the majority of knives won’t benefit from this sharpening angle, an edged tool like a machete, cleaver or ax must be durable (and can be made of softer steel) and can respond to a 30-degree angle.”

We can trust that the electric shaver manufacturers are making products to obtain the best customer satisfaction—including the convenience of rarely needing to replace blades—by making their systems as specified. They have used the same patents for decades and have a fairly transparent and logical motive to follow.


Critique No. 7

Your thesis boils down to basically, maybe, we can determine that all blades in all rotary shavers are never sharp enough to cut by themselves.


Response to Critique No. 7

Our position is that overwhelming evidence proves that blade sharpness is irrelevant to the functioning of electric shavers since even if they are dulled, they function just the same. Electric shavers are designed to work as scissors—not as razors—since manufacturers prioritize durability.


Critique No. 8

Rotary shaver blade sharpeners and replacement blades are available on the internet. Electric shaver blades’ sharpness matters, showing they possibly function as a razor.


Response to Critique No. 8

Electric shaver blades’ sharpness does moderately impact their effectiveness. The same applies to scissors which need to be sharpened periodically. Just because electric shaver blades function better when sharp, does not prove they do not work as scissors. However, it seems that most men do not sharpen their electric shaver blades, since they function satisfactorily without intervention.


Critique No. 9

There is another factor—blade width at the point. Sharpness is thought to be primarily impacted by blade angles and width. See attached and some links below:


Sharpness vs Cutting Ability



Response to Critique No. 9

The discussion regarding blade width focuses on wear on the edge. A factory blade or any properly sharpened blade will have a width of barely a few microns. Blade width is not a halachic concern because if the tests from Philips-Norelco use factory-new blades, that is the best they will ever cut in terms of width. We may safely assume that if the factory width is insufficient to cut in their tests, increasing the width with the shaver will only increase the reliance on the second blade. If factory-new blades always require a screen to cut, they will continue to need it as they wear down.


Critique No. 10

Rav Yisrael Meir Morgenstern—in his HaNoi V’HaNetzach (pages 52-53)—cites a study by Rav Eliyahu Deri, arguing they have conducted experiments demonstrating that electric shaver blades cut without the partnership of the screen.


Response to Critique No. 10

Rav Deri and Rav Morgenstern ambitiously claim that the patents and information from top engineers from Gillette and Philips-Norelco are inaccurate. Rav Morgenstern briefly describes the experiment conducted to prove this claim. However, without a formal description and a recording of their investigation, it is difficult to scrutinize and assess whether the experiment accurately recreates an electric shaver blade cutting facial hair. Absent such a formal study to match those of the companies and top engineers, there is no more reason to accept Rav Deri’s claims than not to admit them. We cannot replicate and test their experiment without such documentation. As such—until such documentation
and explanation are provided—Rav Deri and Rav Morgenstern’s claims enjoy no halachic credibility or validity.

Professor Zarembski concurs: He wrote, “I share your response to critique no. 10; I am always wary of an ‘ad-hoc’ test that lacks a proper technical description of the process, especially when it contradicts very strong evidence.”



We have successfully responded to all of our critiques and are even more convinced of our position. Until the electric shaver patents and technology change, there is no concern that the current information will become outdated. Our rebbeim—Rav Hershel Schachter and Rav Mordechai Willig—agree. Professor Zarmebski kindly reviewed our responses and confirmed the accuracy of our engineering assertions.

Rabbi Jachter serves as the Rav of Congregation Shaarei Orah, a Rebbe at Torah Academy of Bergen County, and a Get administrator with the Beth Din of America. His sixteen books, including a brand new one on Sefer Devarim, are available on Amazon.

Leave a Comment

Most Popular Articles