Aside from pet chews getting all gooey and messy after the dog has been chewing on them a while, are they safe for your pet?
Fresh animal hides, the material of most chews, must be preserved, the hair removed and the hides cured to prevent spoiling. Many of the least expensive chews come from Asia where no restrictions are put on this process.
Poorly processed animal hides can contain lead, arsenic, mercury, chromium salts and formaldehyde. USDA only requires an import license and certificate of origin. US products may be safer but they also use chemical processing.
If you must buy pet chews, buy man made materials or a high grade product that states that it is naturally processed and made in USA.