Parabens

The toxicity of SLS is unconfirmed. The most that research papers say is that it is a skin irritant. Then again, there are very few studies on clinical effects of longterm topical exposure to SLS. In the lab, we know that SDS causes respiratory problems if it's breathed in and someone wrote on a recipe card (for making the SDS solution) that SDS is carcinogenic. Then again, we use ethidium bromide (EtBr) in the lab and it is carcinogenic. And I've touched that buffer plenty of times (on accident)...

So I looked into parabens. Wiki talks about low estrogenic activity of parabens and how it is found in breast tumor tissue, but that doesn't lead to any legitimate conclusions. I looked at PubMed.com, where all biological research papers (including public health, toxicology, and psychology) are databased. There are numerous studies on parabens, and I'm reading one of the articles right now. This review basically says that the parabens do enter your skin and bloodstream, and parabens and their metabolic byproducts have been found in human blood and urine samples. There are esterases in your skin that can break down the parabens, but they are easily saturated, so most of the parabens that are absorbed through your skin are not metabolized (or broken down).

There are many compounds with estrogen-like activity, and these are known as oestrogens. Parabens have weak oestrogenic activity, meaning they cause some of the same effects as estrogen and bind to the same receptor.

Epidemiological, clinical and experimental studies over more than a century cofirm that oestrogen plays a central role in the development, progression and treatment of breast cancer (Miller, 1996; Lonning, 2004), which brings into question potential interactions from environmental chemicals which can enter the human breast and which can mimic oestrogen action. All the widely used paraben esters have now been shown to possess oestrogenic activity in assay systems in vitro [cellular assays] and in vivo [animal studies] and a list of the many studies from different laboratories was published in 2004 (Harvey and Darbre, 2004), updated in 2006 (Harvey and Everett, 2006) and has been further updated here.

...In addition, studies have shown that the common metabolite of paraben esters phydroxybenzoic acid (see Fig. 1) also possesses oestrogenic activity in both in vitro and in vivo assays (Table 2). Thus, whilst shortening of the alkyl [CH2 chain] group in the paraben ester was already known by 2004 to reduce oestrogenic activity, more recent work has shown that complete removal of the alkyl grouping reduces activity still further but does not eradicate all oestrogenicity.

The article goes on to talk about how, even though parabens have weak oestrogenic activity that could have little clinical implications, there has to be more work done to look into whether or not parabens could reach full agonist response with lower concentration over longer period of time. They then went on to look at anti-androgenic activity of parabens in male reproductive systems. Lastly, the article talks about a potential role of parabens in skin cancer:

...methylparaben and ethylparaben can induce oxidative stress in skin after reaction with singlet oxygen (O2) in visible light... However, the report that methylparaben potentiates UV-induced damage of skin keratinocytes ... poses more serious questions concerning potentially genotoxic effects of methylparaben applied in cosmetics to human skin when exposed to sunlight. This is important in the context of the use of methylparaben in sunscreen products and the continued uncertainty as to whether there is a positive or negative association between sunscreen use and development of human skin cancers.

So yeah, that's enough for me to avoid parabens. And I don't need any further skin troubles, so no SLS either. I think I should also look into plant oils and the stuff they use in paraben-free, SLS-free products to see if they have any toxicity issues similar to these compounds.