What it is
Butylphthalimide is a small phthalimide ester that acts as a plasticizer. When combined with film-forming polymers, it softens the resulting film so it remains flexible and less prone to cracking. It is commonly paired with a related plasticizer such as isopropylphthalimide in cosmetic formulas.
Safety & warnings
Used at low levels as a plasticizer, this ingredient is generally well tolerated and is not a recognized common allergen. It is a phthalimide and is chemically distinct from the phthalate esters that have drawn separate regulatory attention.
Origin & sourcing
Synthetic; an organic phthalimide compound.
Questions everyone asks
What is a plasticizer doing in a sunscreen?
It keeps the film left by film-forming polymers flexible, so the layer stays smooth and resists cracking on the skin.
Is butylphthalimide a phthalate?
No. It is a phthalimide, a chemically distinct compound from the phthalate esters often discussed in cosmetic safety.