Can I use tretinoin on my legs/thighs to get rid of razor bumps/ingrown hairs?

Tretinoin is unlikely to be helpful in this situation and does come with the risk of causing irritation. I recommend a benzoyl peroxide wash and a  topical antibiotic like clindamycin +/- oral antibiotics to the initial bumps down followed by laser hair removal to prevent them in the future. 

Thank you for your question,When treating inflamed skin it is best to avoid touching or shaving the area. Choosing products that are soothing are best. 

Thank you for your question.Tretinoin is a retinoid topical medication that is used to treat comedonal acne. Razor burn or ingrown hairs are better treated with topical antibiotics and benzoyl peroxide washes. Common side effects of tretinoin is redness, irritation, peeling, dryness, etc. I highly recommend you consult with a board certified dermatologist to have your skin evaluated and to discuss appropriate treatment options. Take care and good luck.