They absolutely do. The scalp is one of the most vascular and permeable areas of the body. These blood vesels move straight down the carotid artery. Secondly, molecular mass (the too big assumption) is measured in Dalton's... anything under 1,000 is absorbable and under 500 Dalton is considered to be easily, and highly absorbed by the dermis. An example: Isopropanol
(isopropyl alcohol) is about 60 daltons, and is a common carrier used in solvent based adhesives. Meaning molecules over 8x (800%)
larger than the molecular size of the most common ingredient used in hair system acrylic adhesives can still pass. Heptane another very common ingredient is around 100 Dalton.... Toulene is 90.... Ethyl acetate a mere 88 Dalton ....all commonly used, easily absorbed, and will enter the blood stream through your skin.
AND.....Are you ready? Thats the complete list of ingredients, for the most popular, well known, and most commonly used, acrylic hair system adhesive....
Walker Ultra Hold...
Ultra Hold™ cleans up quickly for a liquid adhesive and one of the most reliably long-lasting holds on the market.
Silicone is similar because it uses Ethyl acetate.... Even the safer of the three, being "water-based", is not free from absorbtion. Always remember, polymer is what plastic is derived from, and "co" simply means comprised of more than one type. If we could break down those ingredients, I'm confident we'd come to the same conclusion as solvent based adhesives...
The broad term "acrylic polymers" is much like stating "proprietary blend". Without knowing exactly what's in it, I cannot give a range of numbers. Nevertheless, on average, acrylic is approximately 300 Dalton.....far below the maximum threshold of absorbability......and It would be foolish to believe it's not absorbed.