本生反应（英语：Bunsen Reaction）是一个使水、二氧化硫和碘互相混合并产生无机硫酸及碘化氢的化学反应，以德国化学家罗伯特·威廉·本生命名。他是硫—碘循环（英语：Sulfur–iodine cycle；一个用来产生氢气之化学循环）的第一步，并常在120°C高温中进行。该反应的化学反应方程序如下：

2H₂O + SO₂ + I₂ → H₂SO₄ + 2HI

另外，与这个反应相近的化学反应有卡尔·费休滴定法（英语：Karl Fischer titration）。

The Bunsen reaction is a chemical reaction that describes water, sulfur dioxide, and iodine reacting to form sulfuric acid and hydrogen iodide:

This reaction is the first step in the sulfur-iodine cycle to produce hydrogen. The products separate into two aqueous layers, with the sulfuric acid floating on top, and a mixture of hydrogen iodide and unreacted iodine on the bottom. While the two layers are generally considered immiscible, small amounts of sulfuric acid may still remain in the hydrogen iodide layer and vice versa. This can lead to unwanted side reactions, one of which precipitates out sulfur, a potential obstruction to the reaction vessel. The reaction is named after Robert Bunsen, who discovered it in 1853.