Related question:
I've heard people say that holding it in will "crystalize your lungs," which is obviously bullshit. Is there any significant health risk increase from holding a hit rather than blowing it out right away?
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Sorry, I didn't UTFSE. I did some looking around, and it appears that this is a myth. Fairnymph confirmed this, and I trust her advice on health-related issues since she is studying medicine. If you drew it into your lungs to begin with, why not hold it and absorb more?