Monday, March 15, 2010

Chemistry of skin: Sebum

Sebum can be our friend when it is protecting our skin from infection or fungi, protecting from friction, and reducing TEWL, but it can be our enemy when it's causing us shiny skin and acne pustules!

As you can see from this picture, sebaceous glands are located in the hair follicles of our body. The sebum is secreted here, then attach to the hair and migrate to the surface of our skin. Sebum is composed of about 25% wax, 41% triglycerides, 16% free fatty acids, and 12% squalane. It is a good source of Vitamin E, which can help with retarding oxidation of those fatty acids and provide some subcutaneous skin protection (underneath our skin).

When these wonderful lipids reach the surface, they change. The triglycerides are hydrolyzed to produce glycerine and free fatty acids (you soap makers might recognize this as saponification!) and the cholesterol is esterified (which sometimes offers that recognizable smell of oily hair or skin). These free fatty acids contribute to the acidity or pH of our skin surface. At the surface, the sebum blends with the stratum corneum lipids to produce a lipidic film that covers our skin.

We have sebaceous glands all over our body - except the palms of our hands and the soles of our feet - and the most active are found on our head, face, neck, shoulders, and thorax (don't I know this!). Hyperseborrhea, meaning too much oil produced, can be a function of the number of glands and how much they produce. Our sebum production is dependent on our genetic make-up, endocrine system, and environmental factors. We rarely produce sebum before age 7. It increases through adolescence, then declines until about age 50.

As a note, if you're over 50 and find you have dry eyes, this is because the Meibomian glands (modified sebaceous glands in our eyes that act as tear evaporation preventers) have reduced their sebaceous output. Apparently glycerin works really really to re-hydrate your eyes. Obviously not a diagnosis or treatment plan, just something I read recently.

Sebum can be a royal pain in the bum for those of us who produce too much of it, but it does serve a great purpose! It can help protect our skin from environmental and chemical insult, help protect against bacteria and fungi, and keep us looking younger (the oilier the skin, the fewer wrinkles we tend to produce). It makes our skin wettable as it is a natural surfactant, allowing oils and water to mix so we can clean our skin and hair.

Interestingly enough, although it can help reduce trans-epidermal water loss, it doesn't actually have an effect on how hydrated our skin can be. We can have really oily skin, but still show signs of dryness (itching and flaking, for instance). If you find yourself in a position of having oily skin that is really dry, glycerine is the answer! Yep, a lotion or gel containing a lot of glycerine really helps increase skin hydration and plasticity.

But it's not all hearts and flowers with sebum. (Check out this post on comedogenicity and acnegenicity to see the mechanisms of acne! I'm sure you don't want me to copy the entire thing here!)

If you have too much oil, I'm sorry to say there are no creams or lotions you can create that will reduce the amount of sebum you are producing in your skin or hair. The studies to date on over-production of sebum are inconclusive when it comes to topical products, except for retinols. The best idea of those of us who are normally to hyper-oily is to cleanse our hair or skin with mild cleansers. If we use harsh detergents, we can strip too much oil away and it will only come back a little quicker. Mild cleansing, followed with something nice to soothe our skin (if necessary) like a toner or oil-free moisturizer, is the key. For oily hair, mild cleansing followed by a non-oil containing conditioner is the best idea. (I'll get more into the details of this in a few days when we look at the oily skin type!)

Join me tomorrow as we take a look at different skin types and how we can create awesome products that will work with each one!


Carol said...

I love your blog. I learn so much about crafting bath and body product here.

You mentioned that sebum is a natural surfactant. I am really lost, could you explain more? Oh what is the HLB of sebum then? :)

About glycerin, this is from the 'Handbook of Cosmetic Science' Chapter 9.
'Glycerol also prevents the
crystallization of stratum corneum lipids at low relative humidity, which leads to less TEWL
and higher water content of the skin. ' You probably have read this book, just thought to share. I borrowed this book from library just out of interest, but never really understand the contents. Your blog is my savior.

'Apparently glycerin works really really to re-hydrate your eyes. ' Is this still undergoing research? Or it is being available as remedy for dry eyes already? Just curious.

Topcat said...

Thank you - I am looking forward to your next post! :)

Susan Barclay-Nichols said...

I'll be getting into surfactants in the near future, but for now - a surfactant is something with a hydrophilic (water loving) end and a hydrophobic (water hating) end. Emulsifiers are surfactants - they bring the water and oil together because one end loves the water and one end loves the oil. So sebum has a water hating end and a water loving end to connect water and oil together.

As for using glycerin, if you look at eye drops, they can contain glycerin and/or propylene glycol. (We have some Visine and it contains both.) The eye wash my husband is using this week (he has an irritated eye!) contains witch hazel, glycerin, and benzalkonium chloride (that new stuff they're putting into hand sanitizers). So to answer the question - yes, they are using it in all kinds of eye related things.

But please don't make your own eye related things! You can't be too careful when you're sticking things in your eyes!

elena said...

I have a friend who swears by bergamot essential oil for controlling sebum production. She uses grapeseed as the carrier, because it is a very astringent oil, and about 3 or 4 % bergamot EO (bergaptene free! otherwise you get photosensitive), and just pats it on damp skin.

Susan Barclay-Nichols said...

Hi Elena. That makes sense. Bergamot is a member of the citrus family (and awesome in my Earl Grey tea!) so it is astringent. And it would smell just lovely. I wonder how it would go in my equal parts rosemary-sage-cedarwood-lime or lemon essential oil blend for my hair?

Thanks for reminding us it can make you photosensitive. I didn't remember that when I used it in a lip balm a few years ago!

Anonymous said...

hi thanks for the post! it answered my question as to why sebum wasn't artificially put into lotions since my textbook said it "prevented dry brittle crackled skin" but anyways you sound pretty knowledgeable do you know of a good lotion for dry skin?


Susan Barclay-Nichols said...

Hi Anonymous. Please check the section on skin chemistry for more on dry skin, or do a search for "dry skin". There's a lot on this blog on that topic.

Rose said...

I know I'm just reading this over a year later, but to anonymous, jojoba oil is great for dry skin. It has 96% (Or so) ceramides which is great for dry skin. I have been trying this on my daughter who has severe eczema. I have her on a strict WO regime. After showering, she adds jojoba to damp skin. A little goes a long way. It has taken all of three weeks, but her skin looks great! I wish I had known this when I was her age. Hope this helps.

Susan Barclay-Nichols said...

Hi Rose. What do you mean 96% ceramides? I'm afraid this doesn't make sense to me. And have you considered using a humectant for your daughter's skin? Dry skin needs hydrating more than occlusion, and humectants are the only way to hydrate!

Unknown said...

Hi Susan, that's what I have always been told. I know that there is validity to that, but my mind has been blown away by this new research. To begin, I took my daughter to a dermatologist for something totally unrelated (her hair started falling out) after the doctor looked at her for that, she said so, what are you doing for your daughters eczema? (It was pretty bad at the time; both arms, legs, under the neck, and stomach.) I told her we just keep her away from things that she is allergic to and the occasional use of a topical steroid when it's really bad, which is, at most, twice a year. Other than that we always use humectants, they work, but doesn't stop her skin from having break outs. She began to tell us about new research in dermatology about the use of ceramides on the skin. I didn't know what that was. She explained (I have also done some research at the library and online) ceramides are a form of lipid. It helps to keep the skin moisturized and helps to keep the skin in balance. She gave us some samples and sent us on our way. One has oat in the ingredients and she is allergic so that is out. The other two, although trusted brands, I didn't like the ingredients so I did more research to find other things that have ceramides, but more natural. She also stated that the lotions she gave us had about 40% ceramides. In my research, I have found that jojoba has at least 96% ceramides, plus it's the closest to our skins natural oils. I have her put the jojoba on after she showers and I will tell you that her skin has cleared dramatically. This time of the year because of the heat and allergens in the air she has breakouts until at least the end of August. We were both amazed at this. I did find a link online that I thought was useful. Since you have a science background, you will probably find this useful.
Also a YouTube page that the doctor suggested I look at to explain a little bit more.

What are Ceramides?:

Also, I have been WO since November and have been using jojoba on my own skin. I chose jojoba because coconut oil broke me out into hives on certain parts of my body (I have very sensitive and dry skin. I have had this problem all of my life) I went WO because I would break out into hives pretty much every day. I've tried all soaps for sensitive skin and dry skin. I have also used items that are hypo allergenic as well as non comediogenic. Nothing has ever helped.

In the video that I have sent you, there's a pic of someone with dry skin, my skin looked 10 times worse than that. If there's truth to ceramides and how it can help to keep the skin in balance, I would have to agree. My skin has been in the best health of my life. No dry patches, no eczema, no itchy skin, no dry cracks in my skin.... They are totally gone.

If you can explain this better to the reason why it works, that would be wonderful.

Sorry that this post is so long.
Have an amazing day