This is the third installment in my Mad Scientist series, where I try to make sense of the published scientific literature on shaving.
My previous articles [1, 2] looked at the scientific data on softening and cutting beard hair. They concluded that water absorption is the only important factor in making beard hair easier to cut. Other factors such as pH, temperature, keratin, soaps and detergents, and the cuticle have no practical effect. But these conclusions seem to disagree with the practical experience of many people. Clinical studies and practical experience suggest that using lather is more effective than plain water alone.
One way to look at this discrepancy is to note that the scientific tests were all done in in vitro (i.e. in the lab) with the hair already removed from the face.
One is immediately confronted with the possibility that the water in those tests may have penetrated the hair through its length from the cut end. If so, a proper test would need to either waterproof the cut ends, or dip the hairs in water being careful not to immerse the cut end. It's not clear that any of the tests account for this possibility.
The in vitro cuts were all done at some distance from where the hair is mounted. In vivo (i.e. live, or on the face), hairs are cut at or below the skin line. Friction of the blade against the face was never considered in these in vitro tests. (Nor will it be discussed here.) But it is probably significant that a blade cuts about as much skin as hair.
But putting all of that aside, we're still confronted with the fact that a razor cuts hair at or below the skin level. Since the skin surrounding the hair follicle is often raised above the normal level of skin, we may as well accept that a razor often cuts below the level of skin. Below the skin level, water absorption could easily be inhibited by skin, sebum, and other substances.
Removing skin while shaving is clearly undesirable. Anything we can do to reduce the amount of skin loss will also reduce irritation. In fact, irritation is usually defined in terms of the quantity of skin lost or cut through. Reduced irritation also allows for a closer shave with fewer issues, such as ingrowns.
While a practical goal for shavers might be to find ways to reduce the amount of skin shaved off, this discussion doesn't go that far. It's enough for now to just establish the basic differences between cutting a free floating hair in vitro and the more complicated case of cutting a hair in vivo. Specifically...
Shaving removes about as much skin as hair.
"Factors Involved in Satisfactory Shaving"[3] reported that the amount of skin removed varies significantly day to day for any person, while the amount of hair removed is generally the same day to day. Typically, the amount of skin removed is about the same as the amount of hair, though it varies from half as much to double the amount. When they examined freshly shaved skin, they found the trauma was mostly caused by removal of the horny layer of skin, mostly around the opening of the hair follicle. The trauma increased when (1) using a new blade, (2) using a thin lather or plain hot water, (3) when stretching the skin excessively, (4) when shaving against the grain, (5) when shaving over an area more than once, (6) when using increased pressure, or (7) shortening the preparation time. Note how many of the factors that make for a closer shave also increase trauma. They single out blade sharpness and effective blade angle as the largest contributors to gross trauma. (A sharp blade or angle above 40 degrees is more traumatic.) They also note that trauma is reduced when the time between shaves is increased to two or more days. Finally, stiffer latherless creams tended to protect skin better.
Several other studies support these conclusions.
"Shaving I. Study of Skin and Shavings"[4] took this further by analyzing the shavings. They concluded that the worst damage consists of scaling (small pieces cut away) and erythema (redness) mostly around the hair follicle opening. They also noted that it wasn't unusual to find large fragments of several hundred cells. Some of these larger fragments were shaped like doughnuts, sometimes containing hairs in the center of the doughnut. These single cells and small clumps confirm the earlier studies.
They go on to talk about the absence of a granular layer of skin, the presence of an unusual amount of nucleated cells (cells that have an intact nucleus), and parakeratosis.[5] According to Wikipedia[6], parakeratosis "is associated with the thinning or loss of the granular layer and is usually seen in diseases of increased cell turnover, whether inflammatory or neoplastic." So they suggest that shaving causes this abnormal, if benign, skin condition as a reaction to the increased cell turnover. In essence, it's a short cut the skin uses to quickly recover from the daily trauma of shaving.
According to Wikipedia (Keratinocytes)[7], "Wounds to the skin will be repaired in part by the migration of keratinocytes to fill in the gap created by the wound. The first set of keratinocytes to participate in that repair come from the bulge region of the hair follicle and will only survive transiently. Within the healed epidermis they will be replaced by keratinocytes originating from the epidermis." Keratinocytes (along with build up of sebum) are also implicated in causing or worsening acne, shaving bumps, and ingrown hairs. Note that there are two stages of shaving bumps, temporary ones that are simple inflammation from shaving irritation, and the more chronic ones where the hair follicle gets clogged, leading to acne and ingrown hairs. Either way, it's a good idea to skip shaving for a day or two if you experience shaving bumps after shaving. (But the temporary ones often disappear in a few hours or sooner.) This has been recommended by everyone going back way before Hollander & Casselman.
Several interesting pictures are included in the paper, including the doughnut shaped skin pieces cut away from hair follicles, and examples of nucleation and parakeratosis. "Shaving I" make other interesting points. They included both wet shaving and electric razors. Their pictures show that wet shaving cuts hairs at the same angle every time, such that the two end cuts on any hair (cut on consecutive days) are always parallel to each other, regardless of the angle between the cut and the hair shaft. This differs from the previous studies that suggest the direction of cutting (with or against the grain) is responsible for the angle of the cut. They suggest this is because a person probably shaves a particular hair in the same direction each day. They also show the irregular, cracked nature of hair cut with electric shavers.
"Cutting Characteristics of Beard Hair"[8] discusses failure modes, which are the different ways that hair fractures when it's not cut clean through. Two of these failure modes are partial failures, beginning with a clean cut, but finishing with a small crack, either toward or away from the hair shaft. These dominate when the cut is made less than 2 hair diameters away from where the hair is mounted. These failure modes are not mentioned in "Shaving I". This is probably because actual wet shaving on the face is done much closer to the mount (the skin) than was done in these tests. The number of failures and the degree of failure is correspondingly reduced. In truth, the failure modes are detectable in the "Shaving I" photographs, though to a very small, almost negligible degree.
This brings me up to date, and to the efforts being made today by Gillette and others. Much of the effort today is directed at getting better photographs and taking better measurements. These enable more reliable and precise data, repeatable results, and allow more generic concepts to be used.
One consistent feature of the early literature is to attribute the bulk of irritation to trauma of the skin. The trauma is said to be caused exclusively by removal of pieces of skin, whether a single cell or hundreds of cells. Minor irritation is also caused by tugging of hairs. In these earlier studies, nicks and cuts are typically considered separately. Recent technology advances have enabled more comprehensive approaches. Gillette currently focuses on the concept of micro-nicks--small cuts that break through the skin, which may or may not actually remove any cells. The ability to measure micro-nicks is a result of improved technology, particularly the marriage of computers and the miniaturization of cameras (e.g. cell phone camera sensors).
"Insights Into Shaving and its Impact on Skin"[9] shows close-up color photos of beard hairs and the surrounding skin. The skin around the hair follicle is often raised above the level of surrounding skin. This bump is probably what's shaved off to become the doughnut shaped skin fragments. Because the skin is different in different parts of the body, the bumps will vary across the face and body. These bumps are typically larger on the neck than the face because skin on the neck is typically softer than on the face. If the bumps become larger, they become trapped hairs, and eventually ingrown hairs. This occurs more frequently on the neck not only because the skin is softer, but also because the angle of hair growth tends to be shallower on the neck. The skin doesn't have to rise far to trap the entire hair.
In "The Impact of Shaving on Skin Condition"[10], Gillette notes: "When oil, dirt, perspiration and debris build up around the hair follicles of the beard, water penetration into the hair can be inhibited and prevent the razor from cutting optimally."
This brings me right back to the beginning. While "The Impact of Shaving on Skin Condition" is more marketing tool than peer reviewed scientific paper, I accept this premise. If it disagrees with the previous studies on cutting hair, the difference can be attributed to the in vitro nature of those tests. But if those in vitro studies seem to provide invalid conclusions in some areas, they do provide data that isn't yet available from the in vivo studies.
I'll skip the conclusions this time because they seem pretty obvious after some thought. In a nutshell, some people need a facial scrub to clear the hairs away from skin. Soaps or detergents (in creams) help clear away sebum, perspiration etc, at the skin level. And so on.
[1]A Short Survey of Scientific Literature on Shaving
[2]Water Penetration in Keratin Revisiting the Scientific Data on Shaving
[3]Factors Involved in Satisfactory Shaving
[4]Shaving I. Study of Skin and Shavings; Chetty Bhaktaviziam, Md; Herbert Mescon, Md; Alexander G. Matoltsy, Md; Archives of Dermatology; December 1963; Vol. 88, No. 6:874-879. doi:10.1001/archderm.1963.01590240198033
[5]Wikipedia (epidermis): discusses the skin layers and keratinocytes which are responsible for skin healing.
[6]Wikipedia (Parakeratosis)
[7]Wikipedia (Keratinocytes)
[8]Cutting Characteristics of Beard Hair; S. M. Thozhur, et al; Journal of Materials Science, vol. 42, issue 20, pp. 8725-8737
[9]Insights Into Shaving and its Impact on Skin This B&B thread mentions several other recent papers of interest.
[10]The Impact of Shaving on Skin Condition; Gillette; short overview
My previous articles [1, 2] looked at the scientific data on softening and cutting beard hair. They concluded that water absorption is the only important factor in making beard hair easier to cut. Other factors such as pH, temperature, keratin, soaps and detergents, and the cuticle have no practical effect. But these conclusions seem to disagree with the practical experience of many people. Clinical studies and practical experience suggest that using lather is more effective than plain water alone.
One way to look at this discrepancy is to note that the scientific tests were all done in in vitro (i.e. in the lab) with the hair already removed from the face.
One is immediately confronted with the possibility that the water in those tests may have penetrated the hair through its length from the cut end. If so, a proper test would need to either waterproof the cut ends, or dip the hairs in water being careful not to immerse the cut end. It's not clear that any of the tests account for this possibility.
The in vitro cuts were all done at some distance from where the hair is mounted. In vivo (i.e. live, or on the face), hairs are cut at or below the skin line. Friction of the blade against the face was never considered in these in vitro tests. (Nor will it be discussed here.) But it is probably significant that a blade cuts about as much skin as hair.
But putting all of that aside, we're still confronted with the fact that a razor cuts hair at or below the skin level. Since the skin surrounding the hair follicle is often raised above the normal level of skin, we may as well accept that a razor often cuts below the level of skin. Below the skin level, water absorption could easily be inhibited by skin, sebum, and other substances.
Removing skin while shaving is clearly undesirable. Anything we can do to reduce the amount of skin loss will also reduce irritation. In fact, irritation is usually defined in terms of the quantity of skin lost or cut through. Reduced irritation also allows for a closer shave with fewer issues, such as ingrowns.
While a practical goal for shavers might be to find ways to reduce the amount of skin shaved off, this discussion doesn't go that far. It's enough for now to just establish the basic differences between cutting a free floating hair in vitro and the more complicated case of cutting a hair in vivo. Specifically...
Shaving removes about as much skin as hair.
"Factors Involved in Satisfactory Shaving"[3] reported that the amount of skin removed varies significantly day to day for any person, while the amount of hair removed is generally the same day to day. Typically, the amount of skin removed is about the same as the amount of hair, though it varies from half as much to double the amount. When they examined freshly shaved skin, they found the trauma was mostly caused by removal of the horny layer of skin, mostly around the opening of the hair follicle. The trauma increased when (1) using a new blade, (2) using a thin lather or plain hot water, (3) when stretching the skin excessively, (4) when shaving against the grain, (5) when shaving over an area more than once, (6) when using increased pressure, or (7) shortening the preparation time. Note how many of the factors that make for a closer shave also increase trauma. They single out blade sharpness and effective blade angle as the largest contributors to gross trauma. (A sharp blade or angle above 40 degrees is more traumatic.) They also note that trauma is reduced when the time between shaves is increased to two or more days. Finally, stiffer latherless creams tended to protect skin better.
Several other studies support these conclusions.
"Shaving I. Study of Skin and Shavings"[4] took this further by analyzing the shavings. They concluded that the worst damage consists of scaling (small pieces cut away) and erythema (redness) mostly around the hair follicle opening. They also noted that it wasn't unusual to find large fragments of several hundred cells. Some of these larger fragments were shaped like doughnuts, sometimes containing hairs in the center of the doughnut. These single cells and small clumps confirm the earlier studies.
They go on to talk about the absence of a granular layer of skin, the presence of an unusual amount of nucleated cells (cells that have an intact nucleus), and parakeratosis.[5] According to Wikipedia[6], parakeratosis "is associated with the thinning or loss of the granular layer and is usually seen in diseases of increased cell turnover, whether inflammatory or neoplastic." So they suggest that shaving causes this abnormal, if benign, skin condition as a reaction to the increased cell turnover. In essence, it's a short cut the skin uses to quickly recover from the daily trauma of shaving.
According to Wikipedia (Keratinocytes)[7], "Wounds to the skin will be repaired in part by the migration of keratinocytes to fill in the gap created by the wound. The first set of keratinocytes to participate in that repair come from the bulge region of the hair follicle and will only survive transiently. Within the healed epidermis they will be replaced by keratinocytes originating from the epidermis." Keratinocytes (along with build up of sebum) are also implicated in causing or worsening acne, shaving bumps, and ingrown hairs. Note that there are two stages of shaving bumps, temporary ones that are simple inflammation from shaving irritation, and the more chronic ones where the hair follicle gets clogged, leading to acne and ingrown hairs. Either way, it's a good idea to skip shaving for a day or two if you experience shaving bumps after shaving. (But the temporary ones often disappear in a few hours or sooner.) This has been recommended by everyone going back way before Hollander & Casselman.
Several interesting pictures are included in the paper, including the doughnut shaped skin pieces cut away from hair follicles, and examples of nucleation and parakeratosis. "Shaving I" make other interesting points. They included both wet shaving and electric razors. Their pictures show that wet shaving cuts hairs at the same angle every time, such that the two end cuts on any hair (cut on consecutive days) are always parallel to each other, regardless of the angle between the cut and the hair shaft. This differs from the previous studies that suggest the direction of cutting (with or against the grain) is responsible for the angle of the cut. They suggest this is because a person probably shaves a particular hair in the same direction each day. They also show the irregular, cracked nature of hair cut with electric shavers.
"Cutting Characteristics of Beard Hair"[8] discusses failure modes, which are the different ways that hair fractures when it's not cut clean through. Two of these failure modes are partial failures, beginning with a clean cut, but finishing with a small crack, either toward or away from the hair shaft. These dominate when the cut is made less than 2 hair diameters away from where the hair is mounted. These failure modes are not mentioned in "Shaving I". This is probably because actual wet shaving on the face is done much closer to the mount (the skin) than was done in these tests. The number of failures and the degree of failure is correspondingly reduced. In truth, the failure modes are detectable in the "Shaving I" photographs, though to a very small, almost negligible degree.
This brings me up to date, and to the efforts being made today by Gillette and others. Much of the effort today is directed at getting better photographs and taking better measurements. These enable more reliable and precise data, repeatable results, and allow more generic concepts to be used.
One consistent feature of the early literature is to attribute the bulk of irritation to trauma of the skin. The trauma is said to be caused exclusively by removal of pieces of skin, whether a single cell or hundreds of cells. Minor irritation is also caused by tugging of hairs. In these earlier studies, nicks and cuts are typically considered separately. Recent technology advances have enabled more comprehensive approaches. Gillette currently focuses on the concept of micro-nicks--small cuts that break through the skin, which may or may not actually remove any cells. The ability to measure micro-nicks is a result of improved technology, particularly the marriage of computers and the miniaturization of cameras (e.g. cell phone camera sensors).
"Insights Into Shaving and its Impact on Skin"[9] shows close-up color photos of beard hairs and the surrounding skin. The skin around the hair follicle is often raised above the level of surrounding skin. This bump is probably what's shaved off to become the doughnut shaped skin fragments. Because the skin is different in different parts of the body, the bumps will vary across the face and body. These bumps are typically larger on the neck than the face because skin on the neck is typically softer than on the face. If the bumps become larger, they become trapped hairs, and eventually ingrown hairs. This occurs more frequently on the neck not only because the skin is softer, but also because the angle of hair growth tends to be shallower on the neck. The skin doesn't have to rise far to trap the entire hair.
In "The Impact of Shaving on Skin Condition"[10], Gillette notes: "When oil, dirt, perspiration and debris build up around the hair follicles of the beard, water penetration into the hair can be inhibited and prevent the razor from cutting optimally."
This brings me right back to the beginning. While "The Impact of Shaving on Skin Condition" is more marketing tool than peer reviewed scientific paper, I accept this premise. If it disagrees with the previous studies on cutting hair, the difference can be attributed to the in vitro nature of those tests. But if those in vitro studies seem to provide invalid conclusions in some areas, they do provide data that isn't yet available from the in vivo studies.
I'll skip the conclusions this time because they seem pretty obvious after some thought. In a nutshell, some people need a facial scrub to clear the hairs away from skin. Soaps or detergents (in creams) help clear away sebum, perspiration etc, at the skin level. And so on.
[1]A Short Survey of Scientific Literature on Shaving
[2]Water Penetration in Keratin Revisiting the Scientific Data on Shaving
[3]Factors Involved in Satisfactory Shaving
[4]Shaving I. Study of Skin and Shavings; Chetty Bhaktaviziam, Md; Herbert Mescon, Md; Alexander G. Matoltsy, Md; Archives of Dermatology; December 1963; Vol. 88, No. 6:874-879. doi:10.1001/archderm.1963.01590240198033
[5]Wikipedia (epidermis): discusses the skin layers and keratinocytes which are responsible for skin healing.
[6]Wikipedia (Parakeratosis)
[7]Wikipedia (Keratinocytes)
[8]Cutting Characteristics of Beard Hair; S. M. Thozhur, et al; Journal of Materials Science, vol. 42, issue 20, pp. 8725-8737
[9]Insights Into Shaving and its Impact on Skin This B&B thread mentions several other recent papers of interest.
[10]The Impact of Shaving on Skin Condition; Gillette; short overview
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