Why do nipples get hard when they are touched?

Online Answer
When you stimulate your nipples, your nerves tell your muscles in the area to contract, thus hardening your nipples. Your nipples can also become erect when you have a sexually arousing thought. Of course, nipple hardness is just one symptom of arousal. You may be hot and bothered — even subconsciously!.
Related Questions 📌
Montgomery's tubercles are types of oil-producing glands people have on their areolae. They appear as small bumps. Doctors consider Montgomery's glands protective because they produce oil that keeps nipples soft and protects against infection, which is especially beneficial during pregnancy and breastfeeding.
In regard to the men, 51.7% reported that nipple stimulation caused or enhanced their sexual arousal, 39% agreed that when sexually aroused such manipulation increased their arousal, only 17.1% had asked to have their nipples stimulated, and only 7.5% found that such stimulation decreased their arousal..
When you stimulate your nipples, your nerves tell your muscles in the area to contract, thus hardening your nipples. Your nipples can also become erect when you have a sexually arousing thought. Of course, nipple hardness is just one symptom of arousal. You may be hot and bothered — even subconsciously!.