Is it permissible to use a soft jell from a tube on the lips for a herpes viral infection on Shabbat.
Two issues need to be addressed:
Medicine/Treatments on Shabbos: If the condition requires a course of treatment which was begun before Shabbos, or if the condition is such that it causes illness or extreme discomfort, one may treat it on Shabbos. If, however, the condition does not require a course of treatment, and the condition would not render the person involved sick or place him in extreme discomfort, then the treatment should be deferred until after Shabbos.
Application: The method of application depends on the nature of the jell/ointment. If it is fully absorbed by the lips, it is permitted to apply on Shabbos. If the ointment is not fully absorbed, and it requires smoothing over the surface of the lips, then one may not apply on Shabbos in the normal fashion (smoothing over the lips), but can be applied, without smoothing, and then dabbed or wiped away.
Medicine/Treatment: See Shemiras Shabbos Kehilchasah 35:7-8.
Application: If the cream (the same would apply to a non-liquid jell or ointment) is absorbed in the skin, several poskim write that there cannot be an issue of memare’ach (see Daas Torah 328:26; Minchas Yitzchak 7:20), and it would therefore be permitted to apply in cases of medical treatments. For cream/jell that is not absorbed, the act of smoothing the cream on the surface of the skin/lips presents a problem of memare’ach according to a number of poskim (concerning lips, see Chazon Ish 52:16; Shemiras Shabbos Kehilchasah 14:27, 24:13), and the advice given by poskim is therefore to place the cream/ointment on the skin, without smoothing it over, and allowing it to have its effect. [Concerning lips, this is a little more technically complicated.] See also Orchos Shabbos p. 473, who discusses the prohibition of memachek with regard to creams and ointments, yet defers, in a practical sense, to the authorities to prohibit the practice.
The simplest course of action, where possible, would be to apply the jell just before Shabbos, and once again just after.