diff --git a/app/models/outfit.rb b/app/models/outfit.rb
index 98b38744..714f15d2 100644
--- a/app/models/outfit.rb
+++ b/app/models/outfit.rb
@@ -170,52 +170,67 @@ class Outfit < ApplicationRecord
   end
 
   def visible_layers
-    # TODO: This method doesn't currently handle alt styles! If the outfit has
-    # an alt_style, we should use its layers instead of pet_state layers, and
-    # filter items to only those with body_id=0. This isn't needed yet because
-    # this method is only used on item pages, which don't support alt styles.
-    # See useOutfitAppearance.js for the complete logic including alt styles.
-    item_appearances = item_appearances(swf_asset_includes: [:zone])
+    # Step 1: Choose biology layers - use alt style if present, otherwise pet state
+    if alt_style
+      biology_layers = alt_style.swf_assets.includes(:zone).to_a
+      body = alt_style
+      using_alt_style = true
+    else
+      biology_layers = pet_state.swf_assets.includes(:zone).to_a
+      body = pet_type
+      using_alt_style = false
+    end
 
-    pet_layers = pet_state.swf_assets.includes(:zone).to_a
+    # Step 2: Load item appearances for the appropriate body
+    item_appearances = Item.appearances_for(
+      worn_items,
+      body,
+      swf_asset_includes: [:zone]
+    ).values
     item_layers = item_appearances.map(&:swf_assets).flatten
 
-    pet_restricted_zone_ids = pet_layers.map(&:restricted_zone_ids).
+    # For alt styles, only body_id=0 items are compatible
+    if using_alt_style
+      item_layers.reject! { |sa| sa.body_id != 0 }
+    end
+
+    # Step 3: Apply restriction rules
+    biology_restricted_zone_ids = biology_layers.map(&:restricted_zone_ids).
       flatten.to_set
     item_restricted_zone_ids = item_appearances.
       map(&:restricted_zone_ids).flatten.to_set
 
-    # When an item restricts a zone, it hides pet layers of the same zone.
+    # Rule 3a: When an item restricts a zone, it hides biology layers of the same zone.
     # We use this to e.g. make a hat hide a hair ruff.
     #
     # NOTE: Items' restricted layers also affect what items you can wear at
     #       the same time. We don't enforce anything about that here, and
     #       instead assume that the input by this point is valid!
-    pet_layers.reject! { |sa| item_restricted_zone_ids.include?(sa.zone_id) }
+    biology_layers.reject! { |sa| item_restricted_zone_ids.include?(sa.zone_id) }
 
-    # When a pet appearance restricts a zone, or when the pet is Unconverted,
-    # it makes body-specific items incompatible. We use this to disallow UCs
-    # from wearing certain body-specific Biology Effects, Statics, etc, while
-    # still allowing non-body-specific items in those zones! (I think this
-    # happens for some Invisible pet stuff, too?)
+    # Rule 3b: When a biology appearance restricts a zone, or when the pet is
+    # Unconverted, it makes body-specific items incompatible. We use this to
+    # disallow UCs from wearing certain body-specific Biology Effects, Statics,
+    # etc, while still allowing non-body-specific items in those zones! (I think
+    # this happens for some Invisible pet stuff, too?)
     #
     # TODO: We shouldn't be *hiding* these zones, like we do with items; we
     #       should be doing this way earlier, to prevent the item from even
     #       showing up even in search results!
     #
-    # NOTE: This can result in both pet layers and items occupying the same
+    # NOTE: This can result in both biology layers and items occupying the same
     #       zone, like Static, so long as the item isn't body-specific! That's
     #       correct, and the item layer should be on top! (Here, we implement
     #       it by placing item layers second in the list, and rely on JS sort
     #       stability, and *then* rely on the UI to respect that ordering when
     #       rendering them by depth. Not great! 😅)
     #
-    # NOTE: We used to also include the pet appearance's *occupied* zones in
+    # NOTE: We used to also include the biology appearance's *occupied* zones in
     #       this condition, not just the restricted zones, as a sensible
     #       defensive default, even though we weren't aware of any relevant
     #       items. But now we know that actually the "Bruce Brucey B Mouth"
     #       occupies the real Mouth zone, and still should be visible and
-    #       above pet layers! So, we now only check *restricted* zones.
+    #       above biology layers! So, we now only check *restricted* zones.
     #
     # NOTE: UCs used to implement their restrictions by listing specific
     #       zones, but it seems that the logic has changed to just be about
@@ -232,14 +247,16 @@ class Outfit < ApplicationRecord
       item_layers.reject! { |sa| sa.body_specific? }
     else
       item_layers.reject! { |sa| sa.body_specific? &&
-        pet_restricted_zone_ids.include?(sa.zone_id) }
+        biology_restricted_zone_ids.include?(sa.zone_id) }
     end
 
-    # A pet appearance can also restrict its own zones. The Wraith Uni is an
-    # interesting example: it has a horn, but its zone restrictions hide it!
-    pet_layers.reject! { |sa| pet_restricted_zone_ids.include?(sa.zone_id) }
+    # Rule 3c: A biology appearance can also restrict its own zones. The Wraith
+    # Uni is an interesting example: it has a horn, but its zone restrictions
+    # hide it!
+    biology_layers.reject! { |sa| biology_restricted_zone_ids.include?(sa.zone_id) }
 
-    (pet_layers + item_layers).sort_by(&:depth)
+    # Step 4: Sort by depth and return
+    (biology_layers + item_layers).sort_by(&:depth)
   end
 
   def wardrobe_params
diff --git a/spec/models/outfit_spec.rb b/spec/models/outfit_spec.rb
index ef8bffb9..68370485 100644
--- a/spec/models/outfit_spec.rb
+++ b/spec/models/outfit_spec.rb
@@ -8,7 +8,7 @@ RSpec.describe Outfit do
 		pet_state = PetState.create!(
 			pet_type: pet_type,
 			pose: pose,
-			swf_asset_ids: swf_assets.map(&:id)
+			swf_asset_ids: swf_assets.empty? ? [0] : swf_assets.map(&:id)
 		)
 		pet_state.swf_assets = swf_assets
 		pet_state
@@ -376,5 +376,171 @@ RSpec.describe Outfit do
 				expect(layers).to eq([background, bg_item, hat_asset, body_layer, shirt_asset, head_layer])
 			end
 		end
+
+		context "alt styles (alternative pet appearances)" do
+			before do
+				# Create an alt style with its own body_id distinct from regular pets
+				@alt_style = AltStyle.create!(
+					species: species(:acara),
+					color: colors(:blue),
+					body_id: 999, # Distinct from the regular pet's body_id (1)
+					series_name: "Nostalgic",
+					thumbnail_url: "https://images.neopets.example/alt_style.png"
+				)
+			end
+
+			it "uses alt style layers instead of pet state layers" do
+				# Create regular pet layers
+				regular_head = build_biology_asset(zones(:head), body_id: 1)
+				regular_body = build_biology_asset(zones(:body), body_id: 1)
+				pet_state = build_pet_state(@pet_type, swf_assets: [regular_head, regular_body])
+
+				# Create alt style layers (with the alt style's body_id)
+				alt_head = build_biology_asset(zones(:head), body_id: 999)
+				alt_body = build_biology_asset(zones(:body), body_id: 999)
+				@alt_style.swf_assets = [alt_head, alt_body]
+
+				# Create outfit with alt_style
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+
+				layers = outfit.visible_layers
+
+				# Should use alt style layers, not pet state layers
+				expect(layers).to contain_exactly(alt_head, alt_body)
+				expect(layers).not_to include(regular_head, regular_body)
+			end
+
+			it "only includes body_id=0 items with alt styles" do
+				# Create alt style layers
+				alt_head = build_biology_asset(zones(:head), body_id: 999)
+				@alt_style.swf_assets = [alt_head]
+				pet_state = build_pet_state(@pet_type)
+
+				# Create a body-specific item for the alt style's body_id
+				body_specific_asset = build_item_asset(zones(:hat), body_id: 999)
+				body_specific_item = build_item("Body-specific Hat", swf_assets: [body_specific_asset])
+
+				# Create a universal item (body_id=0)
+				universal_asset = build_item_asset(zones(:background), body_id: 0)
+				universal_item = build_item("Universal Background", swf_assets: [universal_asset])
+
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+				outfit.worn_items = [body_specific_item, universal_item]
+
+				layers = outfit.visible_layers
+
+				# Only the universal item should appear
+				expect(layers).to contain_exactly(alt_head, universal_asset)
+				expect(layers).not_to include(body_specific_asset)
+			end
+
+			it "does not include items from the regular pet's body_id" do
+				# Create alt style layers
+				alt_body = build_biology_asset(zones(:body), body_id: 999)
+				@alt_style.swf_assets = [alt_body]
+				pet_state = build_pet_state(@pet_type)
+
+				# Create an item that fits the regular pet's body_id (1)
+				regular_item_asset = build_item_asset(zones(:hat), body_id: 1)
+				regular_item = build_item("Regular Pet Hat", swf_assets: [regular_item_asset])
+
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+				outfit.worn_items = [regular_item]
+
+				layers = outfit.visible_layers
+
+				# The regular pet item should not appear on the alt style
+				expect(layers).to contain_exactly(alt_body)
+				expect(layers).not_to include(regular_item_asset)
+			end
+
+			it "applies item restriction rules with alt styles" do
+				# Create alt style layers including hair
+				alt_head = build_biology_asset(zones(:head), body_id: 999)
+				alt_hair = build_biology_asset(zones(:hairfront), body_id: 999)
+				@alt_style.swf_assets = [alt_head, alt_hair]
+				pet_state = build_pet_state(@pet_type)
+
+				# Create a universal hat that restricts the hair zone
+				zones_restrict = "0" * 36 + "1" + "0" * 20 # bit 37 (Hair Front) = 1
+				hat_asset = build_item_asset(zones(:hat), body_id: 0, zones_restrict: zones_restrict)
+				hat = build_item("Hair-hiding Hat", swf_assets: [hat_asset])
+
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+				outfit.worn_items = [hat]
+
+				layers = outfit.visible_layers
+
+				# Hair should be hidden by the hat's zone restrictions
+				expect(layers).to contain_exactly(alt_head, hat_asset)
+				expect(layers).not_to include(alt_hair)
+			end
+
+			it "applies pet restriction rules with alt styles" do
+				# Create alt style with a layer that restricts a zone
+				alt_head = build_biology_asset(zones(:head), body_id: 999)
+				zones_restrict = "0" * 47 + "1" + "0" * 10 # bit 48 (Background Item) = 1
+				restricting_layer = build_biology_asset(zones(:body), body_id: 999, zones_restrict: zones_restrict)
+				@alt_style.swf_assets = [alt_head, restricting_layer]
+				pet_state = build_pet_state(@pet_type)
+
+				# Create a universal Background Item
+				bg_item_asset = build_item_asset(zones(:backgrounditem), body_id: 0)
+				bg_item = build_item("Universal Background Item", swf_assets: [bg_item_asset])
+
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+				outfit.worn_items = [bg_item]
+
+				layers = outfit.visible_layers
+
+				# body_id=0 items should still appear even in restricted zones
+				# (because they're not body-specific)
+				expect(layers).to contain_exactly(alt_head, restricting_layer, bg_item_asset)
+			end
+
+			it "applies self-restriction rules with alt styles" do
+				# Create alt style that restricts its own horn layer
+				alt_body = build_biology_asset(zones(:body), body_id: 999)
+				alt_horn = build_biology_asset(zones(:headtransientbiology), body_id: 999)
+				zones_restrict = "0" * 37 + "1" + "0" * 20 # bit 38 (Head Transient Biology) = 1
+				restricting_layer = build_biology_asset(zones(:head), body_id: 999, zones_restrict: zones_restrict)
+				@alt_style.swf_assets = [alt_body, alt_horn, restricting_layer]
+				pet_state = build_pet_state(@pet_type)
+
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+
+				layers = outfit.visible_layers
+
+				# The horn should be hidden by the alt style's own restrictions
+				expect(layers).to contain_exactly(alt_body, restricting_layer)
+				expect(layers).not_to include(alt_horn)
+			end
+
+			it "sorts alt style and item layers by depth correctly" do
+				# Create alt style layers at various depths
+				alt_background = build_biology_asset(zones(:background), body_id: 999) # depth 3
+				alt_body = build_biology_asset(zones(:body), body_id: 999)             # depth 18
+				alt_head = build_biology_asset(zones(:head), body_id: 999)             # depth 34
+				@alt_style.swf_assets = [alt_head, alt_background, alt_body]
+				pet_state = build_pet_state(@pet_type)
+
+				# Add universal items at various depths
+				bg_item = build_item_asset(zones(:backgrounditem), body_id: 0)    # depth 4
+				trinket = build_item_asset(zones(:righthanditem), body_id: 0)     # depth 5
+
+				bg = build_item("Background Item", swf_assets: [bg_item])
+				trinket_item = build_item("Trinket", swf_assets: [trinket])
+
+				outfit = Outfit.new(pet_state: pet_state, alt_style: @alt_style)
+				outfit.worn_items = [trinket_item, bg]
+
+				layers = outfit.visible_layers
+
+				# Expected order by depth:
+				# alt_background (3), bg_item (4), trinket (5), alt_body (18), alt_head (34)
+				expect(layers.map(&:depth)).to eq([3, 4, 5, 18, 34])
+				expect(layers).to eq([alt_background, bg_item, trinket, alt_body, alt_head])
+			end
+		end
 	end
 end