An (alleged) extra layer of female fat

Q: Do women really have an extra layer of fat that men don't? (Somewhere, USA)

A: That’s what I hear while shivering: "You shouldn’t be cold because you have an extra layer of fat under your skin."

My motive in answering this question is to drive a stake in the heart of an urban myth. I admit it. And, success is mine. At least, partly.

Checking weight. Courtesy of Wikipedia

"As a former anatomy professor, I can make this simple. . ." emails physiologist Jolie Bookspan, author of Health & Fitness in Plain English. "There is no extra layer in females."

"I checked the assumption about an extra layer of fat with our doc here. Neither of us is aware of an extra layer of subcutaneous fat," says physiologist Jolene H. Bodily of the Institute for Quality Health, the University of Virginia.

Take that, myth! No extra layer!

But then I got to thinking. What if my reader really means: is the fat layer thicker in women than men?  If true, then why do I get so cold?

Figure 2.  A cross section of human skin, showing the first layer called the epidermis ("E" in the diagram), the second layer ("D") called the dermis. The hypodermis, not actually part of the skin, lies immediately below the dermis, and contains the subcutaneous fat. Drawing from Safety Line Institute, State of Western Australia Government, and modified by the author.

Bodily goes on to say, "But women do carry more subcutaneous fat." See Figure 2.

"Women have slightly more subcutaneous fat than men," agrees exercise professor Len Kravitz of the University of New Mexico. "I have never seen a documented study quantifying how much more."

Furthermore, "Males and females are more alike than different," says Bookspan.

That’s what the experts say. My search of medical and biological journals turned up nothing.

Paul Ward of CoolAntarctica.com, however, touches on the central matter: "Subcutaneous fat has a part to play, of course, as an insulator, and women generally have more than men; so it helps them stay warm."

How much difference can a slightly-thicker fat layer make? Apparently, some: "Studies of cold water immersion report lower skin temperature in women than men," says Bookspan. Which figures if women feel colder than men.

But only the surface skin temperature is lower in females, not the deep-skin temperature. "Deep-skin temperatures remained higher compared to those of men under the same laboratory cold conditions (Malkinson, et al., 1981)."

Moreover, the advantage of women in the cold is not just due to fat, says Bookspan. In general, women also squeeze down blood vessels near the surface (vasoconstriction) to a greater extent than men do. Thus, blood flow near the skin is less in women and, therefore, blood temperature and deep-skin temperature is higher. So, when women have cold feet or hands it isn’t necessarily the result of poor circulation. "It's a healthy vasoconstrictive adaptation."

Considering the benefits, it’s OK, I guess, that women feel cold. Our bodies are just adapting to frigid conditions. We women will survive where our male counterparts might perish because of that slightly-thicker fat layer (and squeezed down blood vessels) if we ever encounter life-threatening cold.

Further Reading:

Many are cold but few are frozen by Jolie Bookspan, Dr.JolieBookspan.com

Health & Fitness in Plain English by Jolie Bookspan

Cellulite: Everything you want to know and more by Len Kravitz, "Ask Dr. Len Kravitz

The skin, SafetyLine Institute of Western Australia state government

The skin, Wikipedia

Malkinson, TJ, Martin S, Simper P, Cooper KE. Expired air volumes of males and females during cold water immersion. Can J. Physiol. & Pharmacol 1981; 59:843-846

How humans deal with and survive extreme cold by Paul Ward, CoolAntarctica.com

(Answered April 4, 2006)