The science
The mechanism of a crystal scrub is mechanical removal of loosely attached corneocytes, and the outcome depends on crystal hardness, size and dissolution behaviour, the lubrication of the carrier, and applied pressure. Sucrose crystals are moderately hard and water-soluble, so their abrasive action diminishes over the first minute of use, a self-limiting property that reduces the risk of over-exfoliation; sodium chloride crystals are harder, less quick to dissolve in the oil-rich paste, and provide sustained abrasion, which improves efficacy on hyperkeratotic sites like heels and elbows and increases irritation potential on thin or damaged skin, particularly through the osmotic sting salt produces on micro-abrasions such as freshly shaved skin. Soybean oil, third, is a linoleic-rich triglyceride that lubricates the crystals and leaves a modest lipid film, and glycerin provides some humectancy during and briefly after use.
The formula's distinguishing feature is the inclusion of cocamidopropyl betaine and sodium methyl lauroyl taurate, mild amphoteric and anionic surfactants that emulsify the soybean oil on contact with water, allowing the scrub to rinse without residue. This is functionally a scrub-wash hybrid; the trade-off is that surfactants remove part of the lipid film the oil would otherwise leave, so post-scrub moisturisation matters more than with an oil-only scrub. Shea butter and coconut oil at ninth and tenth contribute minor lipid; at those positions their contribution to skin softness is small relative to the soybean oil.
The botanical extracts have no plausible activity in this format. Carica papaya extract contains papain, a proteolytic enzyme with in vitro keratolytic activity that requires contact time and appropriate pH; Tricholoma matsutake extract is marketed on in vitro tyrosinase inhibition without clinical support; both are present at trace levels in a rinse-off product. Hydrolyzed silk is a film-forming protein of animal origin, aloe powder and tocopherol are minor, and bentonite thickens. Tolerance considerations are the fragrance, with limonene and benzyl benzoate declared as allergens, cocamidopropyl betaine, a recognised contact sensitiser, and the mechanical and osmotic irritation of salt on compromised skin; physical exfoliation is contraindicated on atopic, inflamed, freshly shaved or barrier-damaged skin. SheaMoisture publishes no product-specific testing; the evidence is the general literature on crystal exfoliants and the ingredients' known properties.