The dedication was to St Blaise.
A bull of Pope Urban III of 1186, which listed the churches dependent on the parish church of San Lorenzo in Damaso, probably mentions this one as Ecclesia Sancti Blasi Achariorum. This is the earliest possible historical reference.
Later on, the church had the name de Scorticlariis. The name de Fossa occurs firstly in the 15th century; the word is Latin for ditch or trench. However, alternative contemporary names were de Trivio and alla Pace.
There was a restoration in 1541.
In 1569 it was mentioned as still dependent on San Lorenzo, as it did not have its own font. However, in 1626 it acquired the territory of the suppressed parish of San Nicola dei Lorenesi and became a full parish for exactly a century. Meanwhile, there was another restoration in 1658.
In 1726 the parish was suppressed and the territory divided between Santi Simone e Giuda and San Tommaso in Parione, whereupon the church was restored again and handed over to a confraternity of warehousemen (Confraternita dei Magazzinieri).
By the time of the Nolli map of 1748 the confraternity in possession was known as the Confraternita degli Osti, and the Vasi Itinerary reveals that the members were involved in the wine trade, both wholesale and retail.
The church was deconsecrated during the French occupation, and demolished in 1813 because of its poor condition.
The church was to the west of the south end of the Vicolo degli Osti which preserves the name of the confraternity. The entrance was on this vicolo, and the left hand wall was along the street to the west.
When the church was demolished the opportunity was taken to widen the street and so extend the piazza, so the street frontage of the modern building now there runs approximately along the major axis of the church.
This was a long church in proportion to its width, and was not very small in floor area. There were two pilasters on each side wall supporting the ceiling and flanking the two side altars, and a truly tiny apse which must have been completely filled by the main altar.
The 1658 restoration provided a fresco over the entrance featuring the patron saint, executed by Paolo Guidotti . He was also responsible for the altarpiece of the right hand side altar, depicting St Nicholas Venerating the Madonna and Child, while a disciple of his was responsible for the main altarpiece showing St Blaise Removing a Bone from the Throat of a Child. The left hand side altar had an altarpiece showing Our Lady of Sorrows which was a copy of a work by Annibale Carracci.