SWIM doesn't know about cold causing bumps/blisters/bruises to get any worse, he has never had any get worse due to cold.
SWIY is right about the warm water/cloth bringing veins closer to the skin's surface, making them easier to hit. SWIYs friend may have suggested a warm compress after a shot because if any dope was missed the warmth and the pressure of the compress helps the body tissue absorb the dope that didn't get into a vein.
Methamphetamine is not absorbed by body tissue well, so greater care must be taken to prevent missing. Because the body doesn't absorb
meth very well, missed shots are more susceptible to infection/abcess/etc. than say a missed
heroin/opiate shot.
If a shot of methamphetamine is missed it will be quite painful and the area around the injection site will quickly swell some and turn red. Apply a warm cloth to the injection site and apply pressure, gently kneading/massaging the area. Do this 4-5 times a day until there is no pain, swelling, or redness.
Monitor the area of the miss for signs of infection/abscess. These include:
-Swelling of the area that doesn't stop after a day or two
-Redness around the area that doesn't go away or gets worse
-The area is warm to the touch compared to other parts of the body/skin
-Pus/Discharge from the area
If SWIY thinks the site could be infected it is important to seek medical treatment right away.
Some other better injection techniques:
-New rig every time one is available
-Never, ever share any equipment, especially if touched by anything that has also touched blood
-Wash/sterilize hands/arms/injection site and use as clean of a prep area as possible
-Don't
alcohol swab immediately after injection as this prevents blood clots from forming
-Many, many, many more. Please check the forums and the
documents archive on
IV drug use for lots of other
harm reduction and safer/better injection information.