Learn Spanish (Latin America): Mis manos sudan cuando estoy en un lugar alto. - My hands sweat when I am in a high place.

In Spanish, when you want to talk about a habit, a general fact, or something that happens repeatedly, you use cuando followed by the present indicative tense. Because your hands sweating in high places is a regular reaction rather than a one-time future event, the regular present tense estoy is exactly what you need.

I was taught to use "el" or "la" with body parts instead of "mi" or "mis". Why is it mis manos here?

You usually use definite articles like el or las for body parts when the verb makes it obvious whose body it is, like with reflexive verbs (me lavo las manos for "I wash my hands"). But in this sentence, the hands are the subject doing the action. If you just said las manos sudan, it would mean "hands sweat" in general. Using mis clarifies that you are talking specifically about your own hands.

Wait, is mano masculine or feminine?

Mano is feminine! It is one of the most famous rule-breakers in Spanish vocabulary. Even though it ends in -o, it is always feminine (la mano, las manos). The word mis doesn't change for gender so you can't tell just by looking at it here, but any adjectives describing the hands would need to be feminine, like mis manos frías (my cold hands).

Why use estoy instead of for "I am" in this sentence?