They resent rapid changes in light, temperature or humidity. It can also be the result of being too warm or under-watered. Sometimes there are brown spots on the leaves. Brown spots are the result of either scale or being kept too cold. Scale is a sucking insect and can be easily distinquished from cold damage.
Cold damage is actually in the leaf tissue.
Scale is on the leaf and can be scratched off. Remove as much of the scale as possible and treat with insecticidal soap, pyrethrins or an oil spray. Cold damage is primarily cosmetic and doesn't effect the health of the plant. This is usually a result of being kept too dry, but can even be caused by being too wet, encouraging root rot. Be sure to feed holiday cacti during the summer.