If you use a skill (Medkit for example) you would think that if you used it again it would refresh the duration, however this does not happen.

For some reason it doesn't effect the skill duration so if you use a certain skill and re-use it before the effect is over you may end up in combat while the effect is not active!

You can see what buffs/debuffs are in effect right next to your weapon icon bar.

Skill that you have to wait until effect is done