The answer depends on a lot of factors, but the main one is, “Are you being gentle with yourself?” It also depends on whether you are male or female, not in terms of will you lose sensation, but in terms of what “gentle with yourself” would mean. Many women can masturbate in such a slow and gentle way that the math teacher won’t even notice (except maybe the biting her own lip as she orgasms). Actually there are a whole variety of female masturbation techniques that girls develop depending on what sensations are most pleasurable and basic level of interest. Young teens often discover orgasm almost accidentally interacting with a saddle during riding lessons. Yes, both English and Western saddles CAN give very pleasant sensations, depending on positioning, speed and just plain, what feels good. Unfortunately this is one of the masturbation techniques that can cause a person to develop a “loss of sensation”, not that the person is unable to feel touch, but it can become a preferred type of stimulation which is not “gentle with yourself”. This assumes clitoral orgasm stimulations.
G-spot orgasm masturbation is also a “delicate art”, and for several decades many, if not most, woman claimed that even they could not find their own g-spot. Never use an object harder than an erect penis or a finger for vaginal masturbation. Again, the guideline should be to be gentle with yourself. Using a vibrator can result in a level of intensity of orgasm that is greater than manual stimulation for many women, and some prefer a hard-surface vibrator for this purpose. One should always use caution with any object entering your vagina, which, of course, applies to your favorite penis too.
Some girls (and in fact boys too) need a very rapid stroke to reach orgasm. In both cases the more common tendency is to keep the touch light and rapid, not adding pressure to the clitoris, no extra force behind the thrusts of a dildo or vibrator, nor should there be any tightening of the grip on the penis. Even tiny scratches hurt a good deal in these parts of the anatomy and can take a few days to heal for any but the most minor of irritations.
Guys can also develop “bad” masturbation habits that reduce overall sensitivity. It is not uncommon to use some kind of cloth between one’s hand and the penis. Some delicate and smooth fabric like silk or satin can be pleasant, (avoid seams is a personal recommendation) a double layer of this kind of fabric, one layer sliding over the other gives a very delicate sensation to the skin of the penis. Under some circumstances (e.g. early sexual experiences involve a wool blanket or coarse fabric like denim) frequent masturbation may result in less sensitivity of the skin of the penis. Masturbation with a very full foreskin that is not pulled back to expose the tip (the “glans”) of the penis is less likely to result in desensitizing, but the skin under the foreskin which is usually protected from exposure by the foreskin tends to be quite sensitive and can be more easily irritated than the constantly exposed skin of a circumcised penis. Again, the “rule” should be to be “gentle with yourself.”
The “rule” also applies to manual manipulation of a partner as well. If it is simultaneous and mutual masturbation be careful not to forget to pay attention to your touch on your partner just because your partner is giving you such pleasure. It often takes some practice to reach simultaneous orgasms while being “gentle to yourself and others” too.
I sincerely hope this is some help.