Methods and protocols of harvesting and processing of Porifera species, specifically sponges, and more specifically fresh water species of Genus Spongilla; testing and storing of the processed Spongilla powder; and manufacturing and packaging of Spongilla-based therapeutic compositions for treating and preventing skin diseases are disclosed. Treatable skin conditions and diseases include without limitation acne vulgaris, rosacea, seborrheic dermatitis, psoriasis, photo-aging and actinic keratosis, acne vulgaris, psoriasis, photo-aging, wounds, scars, and eczema (atopic dermatitis).