This is a common point of confusion
Lobinski R

Shampoo: Orgainc Aloe Barbadensis Leaf Juice, Sodium C14-16 Olefin Sulfonate, Cocamidopropyl Betaine, Sodium Cocoyl Isethionate, Glycerin, Caffeine, MSM, Biotin, Pantothenic Acid, PEPTASTEM [Citrus Aurantium Dulcis (Orange) Callus Culture Extract, Centella Asiatica (Gotu Kola) Extract, Tripeptide-5, Palmitoyl Tetrapeptide-7, Acetyl Hexapeptide-8, sh-Oligopeptide1, Allantoin] , Hydrolyzed Keratin, Vitis Vinifera Fruit Cell Extract (Grape Stem Cell), L-Methionine, Myristoyl Pentapeptide-17, Fucus Vesiculosus (Seaweed) Extract, Clitoria ternatea Linn Extract, Niacin, Simmondsia Chinensis (Jojoba) Seed Oil, Brassicamidopropyl Dimethylamine, Arthrospira Platensis, Peppermint (Mentha) Oil, Lavender (Lavendula) Oil, Sage (Salvia officinalis L.) Oil, Bergamot (Citrus Bergamia) Oil, Tocopheryl (Vitamin E), Ethoxydiglycol, Caprylyl Glycol, Xanthan Gum, Guar Hydroxypropyltrimonium Chloride, Sodium Benzoate, Potassium Sorbate, GHK-Cu (Copper Peptide), Radish ferment, Sodium Chloride, Tetrasodium Glutamate Diacetate

For gut health specifically, oral is the preferred route for direct tissue contact
Monthly or less frequent dosing adds further patient convenience differentiation
While Russia and a few CIS states have approved Selank for treating generalized anxiety disorder, the United States Food and Drug Administration (FDA) has not reviewed Selank for any clinical use