What causes numbness in outside thigh?

Meralgia : Most common source of numbness over thigh is secondary to compression of lateral femoral cutaneous nerve, at or near superior iliac crest, and this can cause a mix of pain and numbness over antero-lateral thigh. Might improve with loose clothing over waist and hip. You probably have meralgia paresthetica, less likely lumbar radiculopathy.

Many possibilities: Numbness can occur from various reasons. Some potential causes include nerve damage, nerve compression, vitamin deficiency, alcohol over consumption, side effects of different medications, or as a result of different systemic medical conditions such as diabetes. Get evaluated by a professional to determine the diagnosis. Treatment is based on the diagnosis.