Brief Answer:
yes it can be contagious to use others lipsticks

Detailed Answer:
Hi,good morning
Thanks for asking such a nice question on HCM.
I have read all queries that you asked that some others used product can be allergic or harmful to us and vice versa.
See all this lip sticks contains wax,emollients, pigments like ingredients according to the colour and quality usage,
Now if someone had applied this lipsticks once or more, these lipsticks they came directly in contact with their lips leading to deposition of their cells,bacteria, dust etc on to the tip of lip sticks which might be nonreactive to that person who actually uses it daily means its not allergic to themselves.

When you use their lips stick these particles like dust, bacteria,body tissue come in your contact and our body consider all this as a foreign body or allergen leading to cause immediate immune response like swelling, redness means accumulations of immune mediators like leukotrienes, TNFs,mast cells and get subside automatically after a certain time or taking just antihistamines in one dose.

See, we boys generally never share even shaving brush because it might cause same effects despite knowing that we do not have any kind of infection or allergy.

In a single sentence, others body cells even noninfectious can be a source of allergy for ourselves.

I hope you would now understand the scenario.
Thanks .

---