Permeability/absorption abilities of skin

[Guest guest]

Why is Jojoba wax/oil assimilated by the body so well? I've been using

progesterone cream to regulate my menstrual cycle and it works so

well, I want to know more about the permeability of skin. Why are some

skin problems better served by oral medications or topical ointments?

When we put things on our body which ones are absorbed? How? How fast?

How much? Was my mom right when she said I was poisoning myself when I

wrote with pen ink on my skin? How can those birth control and

nicotine patches work in a time release way?

Is it true that plain water is drying to the skin, wax creates a

barrier on the skin and water/oil emulsions are aborbed? How so?

Well, I've got a zillion questions on this subject, but maybe someone

can get me started in the right direction? Thanks~

[Guest guest]

Thank you Elaine and Maurice! You've given me enough reading to keep

out of trouble for some time! :~) I always figured my mom was lying

about the ink on my skin....but then this progesterone cream works, so

then I was thinking how does this contraption (our skin) work really?

~

[Guest guest]

> Certain substances -can- make

> their way through the maze of lamellar lipid layers and all the other

> skin structures, and eventually end up in the bloodstream. But they

> have to be composed of very small, very light molecules. These are not

> common substances we keep in our cupboards.

I'm not clear on what you mean by common substances we keep in our cupboard=

s.

Certainly many mundane cosmetics products like sunscreens and moisturizers =

penetrate

the stratum corneum.

According to Clin Dermatol. 2001 Jul-Aug;19(4):489-501. Percutaneous absorp=

tion and

delivery systems:

" ...a lipophilic vehicle will easily penetrate facial skin where the SC is =

lipid rich (10–20% by

weight....This membrane (stratum corneum) allows no molecule to pass readil=

y, but nearly

all materials penetrate to some extent. "

In fact, consider the case of sunscreens: " Functional ingredients like UV f=

ilters, for

example, should remain on the skin surface. If they penetrate, they would b=

e beyond their

site of action and so, from a functional point of view, skin penetration of=

these ingredients

is not desired. "

Well:

J Chromatogr B Analyt Technol Biomed Life Sci. 2004 Apr 25;803(2):225-31.

Liquid chromatographic assay for common sunscreen agents: application to in=

vivo

assessment of skin penetration and systemic absorption in human volunteers.=

The purpose of the present study was to develop a reverse-phase high-perfor=

mance liquid

chromatographic (HPLC) assay for quantifying four common sunscreen agents, =

namely 2-

hydroxy-4-methoxybenzophenone, 2-ethylhexyl-p-methoxycinnamate, 2-

ethylhexylsalicylate (octylsalicylate) and salicylic acid 3,3,5-trimethcycl=

ohexyl ester

(homosalate) in a range of biological matrices. This assay was further appl=

ied to study the

skin penetration and systemic absorption of sunscreen filters after topical=

application to

human volunteers. Separation was achieved utilizing a Symmetry C(18) column=

with

methanol-water as the mobile phase. The assay permits analysis of the sunsc=

reen agents

in biological fluids, including bovine serum albumin (BSA) solution, plasma=

and urine, and

in human epidermis. The assay was linear (r2 > 0.99) with minimum detectabl=

e limits of

0.8 ng for oxybenzone, 0.3 ng for octylmethoxycinnamate, and 2 ng for homos=

alate and

octylsalicylate. The inter- and intra-day variation for the four sunscreens=

was less than 3%

at the upper end of the linear range and less than 6% at the lower end. Rec=

overies of

sunscreens from plasma, 4% (w/v) BSA solution and epidermal membranes were =

within the

range of 91-104%. Recoveries from urine of the four sunscreens, and oxybenz=

one with its

metabolites were more than 86%. Up to approximately 1% of the applied dose =

of

oxybenzone and its metabolites was detected in the urine. Appreciable amoun=

ts were also

detected in the stratum corneum through tape stripping. The HPLC assay and =

extraction

procedures developed are sensitive, simple, rapid, accurate and reproducibl=

e. Results from

the preliminary clinical study demonstrate significant penetration of all s=

unscreen agents

into the skin, and oxybenzone and metabolites across the skin.

yikes!

One of the sunscreens I use even has polyacrylamide, which worries me.

> > s it true that plain water is drying to the skin

>

> Not exactly.

Paradoxically, water induces transepidermal water loss, so yes, it can be d=

rying.

> Nothing we make as cosmetic formulators is ever truly absorbed into the

> skin. You wouldn't want it to be.

I make topical antioxidant preparations, and, I do want them absorbed...

[Guest guest]

> Certain substances -can- make

> their way through the maze of lamellar lipid layers and all the other

> skin structures, and eventually end up in the bloodstream. But they

> have to be composed of very small, very light molecules. These are not

> common substances we keep in our cupboards.

I'm not clear on what you mean by common substances we keep in our cupboard=

s.

Certainly many mundane cosmetics products like sunscreens and moisturizers =

penetrate

the stratum corneum.

According to Clin Dermatol. 2001 Jul-Aug;19(4):489-501. Percutaneous absorp=

tion and

delivery systems:

" ...a lipophilic vehicle will easily penetrate facial skin where the SC is =

lipid rich (10–20% by

weight....This membrane (stratum corneum) allows no molecule to pass readil=

y, but nearly

all materials penetrate to some extent. "

In fact, consider the case of sunscreens: " Functional ingredients like UV f=

ilters, for

example, should remain on the skin surface. If they penetrate, they would b=

e beyond their

site of action and so, from a functional point of view, skin penetration of=

these ingredients

is not desired. "

Well:

J Chromatogr B Analyt Technol Biomed Life Sci. 2004 Apr 25;803(2):225-31.

Liquid chromatographic assay for common sunscreen agents: application to in=

vivo

assessment of skin penetration and systemic absorption in human volunteers.=

The purpose of the present study was to develop a reverse-phase high-perfor=

mance liquid

chromatographic (HPLC) assay for quantifying four common sunscreen agents, =

namely 2-

hydroxy-4-methoxybenzophenone, 2-ethylhexyl-p-methoxycinnamate, 2-

ethylhexylsalicylate (octylsalicylate) and salicylic acid 3,3,5-trimethcycl=

ohexyl ester

(homosalate) in a range of biological matrices. This assay was further appl=

ied to study the

skin penetration and systemic absorption of sunscreen filters after topical=

application to

human volunteers. Separation was achieved utilizing a Symmetry C(18) column=

with

methanol-water as the mobile phase. The assay permits analysis of the sunsc=

reen agents

in biological fluids, including bovine serum albumin (BSA) solution, plasma=

and urine, and

in human epidermis. The assay was linear (r2 > 0.99) with minimum detectabl=

e limits of

0.8 ng for oxybenzone, 0.3 ng for octylmethoxycinnamate, and 2 ng for homos=

alate and

octylsalicylate. The inter- and intra-day variation for the four sunscreens=

was less than 3%

at the upper end of the linear range and less than 6% at the lower end. Rec=

overies of

sunscreens from plasma, 4% (w/v) BSA solution and epidermal membranes were =

within the

range of 91-104%. Recoveries from urine of the four sunscreens, and oxybenz=

one with its

metabolites were more than 86%. Up to approximately 1% of the applied dose =

of

oxybenzone and its metabolites was detected in the urine. Appreciable amoun=

ts were also

detected in the stratum corneum through tape stripping. The HPLC assay and =

extraction

procedures developed are sensitive, simple, rapid, accurate and reproducibl=

e. Results from

the preliminary clinical study demonstrate significant penetration of all s=

unscreen agents

into the skin, and oxybenzone and metabolites across the skin.

yikes!

One of the sunscreens I use even has polyacrylamide, which worries me.

> > s it true that plain water is drying to the skin

>

> Not exactly.

Paradoxically, water induces transepidermal water loss, so yes, it can be d=

rying.

> Nothing we make as cosmetic formulators is ever truly absorbed into the

> skin. You wouldn't want it to be.

I make topical antioxidant preparations, and, I do want them absorbed...