You can search by product name, product category, manufacturer, or ingredient. All ingredients in the product are listed along with a safety rating of 0-10 and what type of hazard may caused by the ingredient, as well as a “Data Gap” which indicates the lack of safety information on the ingredient as a percent.
Of course, toxicity is a complex issue and not simple to nail down precisely. It depends on the dosage and the route of exposure (skin, oral ingestion, inhalation, etc). It would be nice to see the actual test data that they used to develop their ratings. Many ingredients are listed as (possible) carcinogens or as neurotoxins, but I can't tell how this was determined. If the actual test were based on oral ingestion or whole cell screens they may not be very informative about how the compound would behave when applied to the skin.
The other problem is dosage – most of the compounds in a cosmetic are likely to be found in small amounts – were the tests done with low concentrations to accurately reflect the “dosage” in a cosmetic? The pigments in particular seem to get the higher toxicity ratings – the thing about pigments is that it only takes a small amount of pigment to get a significant color. It may be difficult to measure the behavior of really small amounts accurately, higher dosages would be easier to measure but may not be good indications of the effects when exposed to only small amounts.
Particularly telling is the “Data Gap” rating which is "is a measure of how much is unknown about an ingredient. " A search for a common shampoo listed one of the ingredients as "Fragrance," which was given a hazard score of 8 (out of 10) with concerns about "Neurotoxicity, Allergies/immunotoxicity, Miscellaneous " and a Data Gap of 100%. The Data Gap score suggests to me that their toxicity rating is a not at all reliable. Most fragrances in commercial products are fairly simple compounds of a floral nature, and probably only present in a fairly small concentration. Although allergy concerns are probably sensible, I really doubt that washing my hair with shampoo is much of a risk for neurotoxic or immunotoxic side effects. Most people with a little common sense would probably tell you the same thing.
Skin Deep is probably a good place to start looking for information about the substances found in cosmetic products, but I don't know how much you should really trust the toxicity ratings that are given.