Cucumbers can contain small amounts of bitter substances, so-called cucurbitacins. They are mainly located at the base of the stem. From this fact, it is often concluded that cucumbers should not be peeled starting from the stalk. Supposedly, the bitter substances would then spread over the entire length of the cucumber.
However, the fact that this actually happens if you peel the cucumber “wrong” has not been scientifically proven and is considered very unlikely. The cucumbers that are commercially available today are also cultivated in such a way that they contain very few bitter substances anyway.
Cucumbers grown in your own garden, on the other hand, can taste bitter from time to time. In this case, however, this cannot be attributed to the peeling technique, but to the soil conditions. The bitter substances are not only found at the base of the stem but under the entire skin. In which direction you then peel such a cucumber does not matter.