Some (not all) cosmetics, like lipstick, are not gluten free. Now you would oh whatever but if you put on lipstick that is not gluten free you can consume some by accident.
Here are some ingredients that are not or may not be gluten free.

AMP-ISOSTEAROYL HYDROLYZED WHEAT PROTEIN
DISODIUM WHEATGERMAMIDO PEG-2 SULFOSUCCINATE
HYDROLYZED WHEAT GLUTEN
HYDROLYZED WHEAT PROTEIN
HYDROLYZED WHEAT PROTEIN PG-PROPYL SILANETRIOL
HYDROLYZED WHEAT STARCH
HYDROXYPROPYLTRIMONIUM HYDROLYZED WHEAT PROTEIN
STEARYLDIMONIUMHYDROXYPROPYL HYDROLYZED WHEAT PROTEIN
WHEAT AMINO ACIDS
WHEAT BRAN EXTRACT
WHEAT GERM EXTRACT
WHEAT GERM GLYCERIDES
WHEAT GERM OIL
WHEAT GERMAMIDOPROPYLDIMONIUM HYDROXYPROPYL HYDROLYZED WHEAT
PROTEIN
WHEAT PROTEIN
WHEAT (TRITICUM VULGARE) BRAN EXTRACT
TRITICUM VULGARE (WHEAT) FLOUR LIPIDS
TRITICUM VULGARE (WHEAT) GERM EXTRACT
TRITICUM VULGARE (WHEAT) GERM OIL
AMINO PEPTIDE COMPLEX
BARLEY EXTRACT
HORDEUM VULGARE (BARLEY) EXTRACT
PHYTOSPHINGOSINE EXTRACT

This information covers products marketed under the following
trademarks: Este Lauder, Inc.; Clinique Laboratories, Inc.; Aramis,
Inc.; Origins Natural Resources, Inc.; Bobbi Brown essentials; Tommy Hilfiger Toiletries, MAC, Stila, and Prescriptives, Inc.

some lip related stuff from Neutrogena are,
Instant Lip Remedy
Lip Boost Intense Moisture Lipstick SPF 20
Lip Boost Intense Moisture Therapy
Lip Moisturizer SPF 15
Lip Nutrition - All
MoistureShine Lip Gloss
Overnight Lip Therapy