Should i be worried that a yellow jacket sting, one week later, is still red, swollen and very itchy?

Yes: I would have a healthcare professional examin if there is an infection.

Depends: Local reactions to bee stings can last for days on end. Typically these reactions appear like the are infected but in reality are very brisk local reactions. You need to check with you doctor to make sure there is no infection that would require antibiotics. I would not be surprised if the just treated you symptomatically.

Is it infected?: Yellow jackets scrounge garbage cans & picnic tables - there's always a worry that their stingers might be contaminated with germs. Considering the number of yellow jacket stings & the few that become infected it's probably not that big a concern. Infections usually hurt rather than itch. Stings will be red & swollen regardless of infection. If you're not sure have a physician take a look.

See Doctor: Although local reactions, which are initially ige-mediated, will naturally involve activated inflammatory cells later, and can last for several days, you should have a health-care professional take a look. Tthere could be other factors contributing to your reaction and why it still has not resolved.

Could be infected: Yellow jacket stings are the most likely hymenoptera stings to become infected. See your doc.

Wasp sting.: When wasps sting, they leave a small portion of the barb in the wound. This foreign body is a protein and it can elicit a strong inflammatory response, characterized by swelling, redness, pain, and itching. Also, it is possible that there is an infection in the site. Either way, a visit to a doctor would be best to determine what is going on.