Can a lip augmentation with Juvederm Ultra plus shrink/dissolve? Even though they are yearly? For instance laying out in the sun

Juvederm is attracted to water, so when you're tanning, you may be dehydrated which appears to shrink the filler. Moisturizing and making sure you drink lots of fluids should give improvement. Hope this helps.

Juvederm is hydrophilic which means it is attracted to water.  When you are dehydrated, your lips will be dehydrated as well.  Therefore, laying out in the sun may indeed make your lips appear smaller in the short term.  Rubbing your lips together frequently may also shorten the life of the Juvederm in your lips.  

This may be due to dehydration which is causing it to appear like your juvederm results are dissolving. I recommend following up with your injector about your concerns. A different filler may yield better results. Implants or fat are an alternative. Best, Dr. Emer

The reason your lips look thinner is because they actually are, because while you're in the Sun your lips become severely dehydrated especially if you do not use sunscreen and a Moisturizer of some kind. Drinking lots of fluids will also help you in preventing that from happening in the future. Lip balm with sunscreen that's SPF 15 or higher is recommendedGoof luck from New York City

Brushing or tanning should not make the juvederm dissipate any faster. Results should last around a year but some patients do metabolize it faster. It’s recommended not to exercise for a day after the filler treatment, otherwise there are no restrictions. 

Tanning in and of itself sets you up for photodamage and risk of skin cancers, so would strongly urge you to sun protect.  In regards to filler, your lip injection from Juvederm Ultra Plus should not contract secondary to the sun.  Lip injections typically last 9 months or longer and as you get injections yearly, there is clinical evidence supporting the fact that collagen can be stimulated, especially in the lips.