The stock fell 1.8% to $102.38 after Credit Suisse downgraded the insurer's stock to underperform from neutral.
Credit Suisse cited adverse weather conditions which have led to losses by the insurer, as well as mounting competition in the home and auto market that has put downward pressure on prices.
In late June, the Northbrook, Ill.-based insurer announced $473 million in "catastrophe losses" for May, up from $290 million in April.
Total losses for May amounted to $504 million, with the amount offset by "favorable reserve reestimates," which helped bring the amount down to $473 million.
Fourteen different weather events drove the May losses, including one Midwest storm that involved tornadoes, hail and wind and which accounted for half the losses that month, according to Allstate.
Second-quarter losses are now up to $763 million, Allstate said on June 20.
The losses come after a tough 2018, in which Allstate took a $2.6 billion hit following even rougher years in 2017 and 2017, when losses caused by storms and other weather events rose 51% and 26% respectively, according to Zacks Investment Research.