When you scan a product and it appears unknown, you can add it directly via the application.
To do this:
1) Scan the product's barcode and click on the "Fill in the information" button.
2) Follow the instructions in the application and take a picture of the requested elements.
If the "Fill in the information" button doesn't appear, it's most likely because it's a product that Yuka is unable to rate (alcohol, nutritional supplements, etc.).
Click here to learn more about products not rated by the app.