A 2015 study of walking lunges and split squats compared leg and hip muscle activity when holding a single dumbbell on the front leg side (ipsilateral) to holding the dumbbell on the back leg side (contralateral).
While activation of the quads was similar in both carrying positions, the glute medius (your upper glutes) was activated to a much greater degree when the dumbbell is held on the back leg side.
In other words, your butt works harder during lunges when you hold a single dumbbell in the hand that's opposite the working leg (i.e. on the same side as the back leg). So, you can maximize glute recruitment when doing lunges by using an offset load while using a forward-leaning torso position.
Now, if your lower-body strength demands you use a weight that's greater than what you're able to hold with one hand, you can still use an offset loading strategy by holding two unevenly loaded dumbbells – holding the heaviest of the two dumbbells on the opposite side of the working leg. So, if you're doing reverse lunges and you're stepping back with your right leg, you'd hold the heavier dumbbell on your right side.
If you're using two unevenly loaded dumbbells, there should be about a 35 to 65 light dumbbell to heavy dumbbell loading distribution. The heavier of the two dumbbells should make up roughly 65 percent of the total weight you're holding. And don't allow your shoulders to rotate or tilt toward the heavier side; keep your shoulders even throughout.